KASAN: slab-out-of-bounds Write in squashfs_readahead (2)

Hello,

syzbot found the following issue on:

HEAD commit:    13d88ac54ddd Merge tag 'vfs-6.7.fsid' of git://git.kernel...
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=121965ef680000
kernel config:  https://syzkaller.appspot.com/x/.config?x=beb32a598fd79db9
dashboard link: https://syzkaller.appspot.com/bug?extid=604424eb051c2f696163
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12b40c7b680000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10f691ef680000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9e81dc4903c2/disk-13d88ac5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f40fd7326b3f/vmlinux-13d88ac5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2f399cd6ff7d/bzImage-13d88ac5.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/8e127c645a04/mount_0.gz

The issue was bisected to:

commit f268eedddf3595e85f8883dc50aed29654785696

Author: Phillip Lougher <[email protected]>
Date:   Sat Jun 11 03:21:32 2022 +0000

squashfs: extend "page actor" to handle missing pages

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1252b717680000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1152b717680000
console output: https://syzkaller.appspot.com/x/log.txt?x=1652b717680000

IMPORTANT: if you fix the issue, please add the following tag to the commit:

Reported-by [email protected]

Fixes f268eedddf35 ("squashfs: extend "page actor" to handle missing pages")

SQUASHFS error: Unable to read metadata cache entry [6fa] SQUASHFS error: Unable to read metadata cache entry [6fa] SQUASHFS error: Unable to read metadata cache entry [6fa]
==================================================================

BUG: KASAN: slab-out-of-bounds in __readahead_batch include/linux/pagemap.h:1364 [inline]
BUG: KASAN: slab-out-of-bounds in squashfs_readahead+0x9a6/0x20d0 fs/squashfs/file.c:569
Write of size 8 at addr ffff88801e393648 by task syz-executor100/5067

CPU: 1 PID: 5067 Comm: syz-executor100 Not tainted 6.6.0-syzkaller-15156-g13d88ac54ddd #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0x163/0x540 mm/kasan/report.c:475
 kasan_report+0x142/0x170 mm/kasan/report.c:588
 __readahead_batch include/linux/pagemap.h:1364 [inline]
 squashfs_readahead+0x9a6/0x20d0 fs/squashfs/file.c:569
 read_pages+0x183/0x830 mm/readahead.c:160
 page_cache_ra_unbounded+0x68e/0x7c0 mm/readahead.c:269
 page_cache_sync_readahead include/linux/pagemap.h:1266 [inline]
 filemap_get_pages+0x49c/0x2080 mm/filemap.c:2497
 filemap_read+0x42b/0x10b0 mm/filemap.c:2593
 __kernel_read+0x425/0x8b0 fs/read_write.c:428
 integrity_kernel_read+0xb0/0xf0 security/integrity/iint.c:221
 ima_calc_file_hash_tfm security/integrity/ima/ima_crypto.c:485 [inline]
 ima_calc_file_shash security/integrity/ima/ima_crypto.c:516 [inline]
 ima_calc_file_hash+0xad1/0x1b30 security/integrity/ima/ima_crypto.c:573
 ima_collect_measurement+0x554/0xb30 security/integrity/ima/ima_api.c:290
 process_measurement+0x1373/0x21c0 security/integrity/ima/ima_main.c:359
 ima_file_check+0xf1/0x170 security/integrity/ima/ima_main.c:557
 do_open fs/namei.c:3624 [inline]
 path_openat+0x2893/0x3280 fs/namei.c:3779
 do_filp_open+0x234/0x490 fs/namei.c:3809
 do_sys_openat2+0x13e/0x1d0 fs/open.c:1440
 do_sys_open fs/open.c:1455 [inline]
 __do_sys_open fs/open.c:1463 [inline]
 __se_sys_open fs/open.c:1459 [inline]
 __x64_sys_open+0x225/0x270 fs/open.c:1459
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f0e73d6c5f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 61 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd516ff158 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0031656c69662f2e RCX: 00007f0e73d6c5f9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000200000c0
RBP: 00007f0e73ddf610 R08: 0000000000000225 R09: 0000000000000000
R10: 00007ffd516ff020 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffd516ff328 R14: 0000000000000001 R15: 0000000000000001
 </TASK>

Allocated by task 5067:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4f/0x70 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:374 [inline]
 __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:383
 kasan_kmalloc include/linux/kasan.h:198 [inline]
 __do_kmalloc_node mm/slab_common.c:1007 [inline]
 __kmalloc+0xb9/0x230 mm/slab_common.c:1020
 kmalloc_array include/linux/slab.h:637 [inline]
 squashfs_readahead+0x30c/0x20d0 fs/squashfs/file.c:552
 read_pages+0x183/0x830 mm/readahead.c:160
 page_cache_ra_unbounded+0x68e/0x7c0 mm/readahead.c:269
 page_cache_sync_readahead include/linux/pagemap.h:1266 [inline]
 filemap_get_pages+0x49c/0x2080 mm/filemap.c:2497
 filemap_read+0x42b/0x10b0 mm/filemap.c:2593
 __kernel_read+0x425/0x8b0 fs/read_write.c:428
 integrity_kernel_read+0xb0/0xf0 security/integrity/iint.c:221
 ima_calc_file_hash_tfm security/integrity/ima/ima_crypto.c:485 [inline]
 ima_calc_file_shash security/integrity/ima/ima_crypto.c:516 [inline]
 ima_calc_file_hash+0xad1/0x1b30 security/integrity/ima/ima_crypto.c:573
 ima_collect_measurement+0x554/0xb30 security/integrity/ima/ima_api.c:290
 process_measurement+0x1373/0x21c0 security/integrity/ima/ima_main.c:359
 ima_file_check+0xf1/0x170 security/integrity/ima/ima_main.c:557
 do_open fs/namei.c:3624 [inline]
 path_openat+0x2893/0x3280 fs/namei.c:3779
 do_filp_open+0x234/0x490 fs/namei.c:3809
 do_sys_openat2+0x13e/0x1d0 fs/open.c:1440
 do_sys_open fs/open.c:1455 [inline]
 __do_sys_open fs/open.c:1463 [inline]
 __se_sys_open fs/open.c:1459 [inline]
 __x64_sys_open+0x225/0x270 fs/open.c:1459
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

The buggy address belongs to the object at ffff88801e393640
 which belongs to the cache kmalloc-8 of size 8

The buggy address is located 0 bytes to the right of
allocated 8-byte region [ffff88801e393640, ffff88801e393648)

The buggy address belongs to the physical page:
page:ffffea000078e4c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88801e393230 pfn:0x1e393
anon flags: 0xfff00000000800(slab|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000800 ffff888012c41280 0000000000000000 dead000000000001
raw: ffff88801e393230 0000000080660063 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 1, tgid 1 (swapper/0), ts 10649202635, free_ts 9358727270
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1e6/0x210 mm/page_alloc.c:1537
 prep_new_page mm/page_alloc.c:1544 [inline]
 get_page_from_freelist+0x339a/0x3530 mm/page_alloc.c:3312
 __alloc_pages+0x255/0x670 mm/page_alloc.c:4568
 alloc_pages_mpol+0x3de/0x640 mm/mempolicy.c:2133
 alloc_slab_page+0x6a/0x160 mm/slub.c:1870
 allocate_slab mm/slub.c:2017 [inline]
 new_slab+0x84/0x2f0 mm/slub.c:2070
 ___slab_alloc+0xc85/0x1310 mm/slub.c:3223
 __slab_alloc mm/slub.c:3322 [inline]
 __slab_alloc_node mm/slub.c:3375 [inline]
 slab_alloc_node mm/slub.c:3468 [inline]
 __kmem_cache_alloc_node+0x21d/0x300 mm/slub.c:3517
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc_node_track_caller+0xa5/0x230 mm/slab_common.c:1027
 kstrdup+0x3a/0x70 mm/util.c:62
 __kernfs_new_node+0x9d/0x870 fs/kernfs/dir.c:611
 kernfs_new_node+0x99/0x170 fs/kernfs/dir.c:679
 kernfs_create_link+0xa5/0x1f0 fs/kernfs/symlink.c:39
 sysfs_do_create_link_sd+0x85/0x100 fs/sysfs/symlink.c:44
 device_create_sys_dev_entry+0x10f/0x170 drivers/base/core.c:3451
 device_add+0x8cf/0xd30 drivers/base/core.c:3595
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1137 [inline]
 free_unref_page_prepare+0x92a/0xa50 mm/page_alloc.c:2347
 free_unref_page+0x37/0x3f0 mm/page_alloc.c:2487
 vfree+0x186/0x2e0 mm/vmalloc.c:2842
 delayed_vfree_work+0x56/0x80 mm/vmalloc.c:2763
 process_one_work kernel/workqueue.c:2630 [inline]
 process_scheduled_works+0x90f/0x1400 kernel/workqueue.c:2703
 worker_thread+0xa5f/0xff0 kernel/workqueue.c:2784
 kthread+0x2d3/0x370 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

Memory state around the buggy address:
 ffff88801e393500: 00 fc fc fc fc fa fc fc fc fc 05 fc fc fc fc 05
 ffff88801e393580: fc fc fc fc 00 fc fc fc fc 05 fc fc fc fc fa fc
>ffff88801e393600: fc fc fc 00 fc fc fc fc 00 fc fc fc fc 00 fc fc
                                              ^
 ffff88801e393680: fc fc 00 fc fc fc fc 00 fc fc fc fc 00 fc fc fc
 ffff88801e393700: fc 00 fc fc fc fc fb fc fc fc fc 00 fc fc fc fc
==================================================================

---
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Before performing a read ahead operation in squashfs_read_folio() and squashfs_readahead(), check if i_size is not 0 before continuing.

[Bug]
path_openat() called open_last_lookups() before calling do_open() and open_last_lookups() will eventually call squashfs_read_inode() to set inode->i_size, but before setting i_size, it is necessary to obtain file_size from the disk.

However, during the value retrieval process, the length of the value retrieved from the disk was greater than output->length, resulting(-EIO) in the failure of squashfs_read_data(), further leading to i_size has not been initialized, i.e. its value is 0.

This resulted in the failure of squashfs_read_data(), where "SQUASHFS error:
Failed to read block 0x6fc: -5" was output in the syz log.
This also resulted in the failure of squashfs_cache_get(), outputting "SQUASHFS
error: Unable to read metadata cache entry [6fa]" in the syz log.

[Fix]
Before performing a read ahead operation in squashfs_read_folio() and squashfs_readahead(), check if i_size is not 0 before continuing.

Quoted 11 lines

[Bug]
path_openat() called open_last_lookups() before calling do_open() and open_last_lookups() will eventually call squashfs_read_inode() to set inode->i_size, but before setting i_size, it is necessary to obtain file_size from the disk.

However, during the value retrieval process, the length of the value retrieved from the disk was greater than output->length, resulting(-EIO) in the failure of squashfs_read_data(), further leading to i_size has not been initialized, i.e. its value is 0.

NACK

This analysis is completely *wrong*. First, if there was I/O error reading the inode it would never be created, and squasfs_readahead() would never be called on it, because it will never exist.

Second i_size isn't unintialised and it isn't 0 in value. Where you got this bogus information from is because in your test patches, i.e.

https://lore.kernel.org/all/[email protected]/

You have

(quoted diff) +6 -0

+	if (!file_end) {
+		printk("i:%p, is:%d, %s\n", inode, i_size_read(inode), __func__);
+		res = -EINVAL;
+		goto out;
+	}
+

You have used %d, and the result of i_size_read(inode) overflows, giving the bogus 0 value.

The actual value is 1407374883553280, or 0x5000000000000, which is too big to fit into an unsigned int.

Quoted 5 lines

This resulted in the failure of squashfs_read_data(), where "SQUASHFS error:
Failed to read block 0x6fc: -5" was output in the syz log.
This also resulted in the failure of squashfs_cache_get(), outputting "SQUASHFS
error: Unable to read metadata cache entry [6fa]" in the syz log.

NO, *that* is caused by the failure to read some other inodes which as a result are correctly not created. Nothing to do with the oops here.

Quoted 4 lines

[Fix]
Before performing a read ahead operation in squashfs_read_folio() and squashfs_readahead(), check if i_size is not 0 before continuing.

A third NO, it is only 0 because the variable overflowed.

Additionally, let's look at your "fix" here.

Review static int squashfs_read_folio(struct file *file, struct folio *folio) · line 468

Quoted 9 lines

(quoted diff) +5 -0

@@ -461,6 +461,11 @@ static int squashfs_read_folio(struct file *file, struct folio *folio)
 	TRACE("Entered squashfs_readpage, page index %lx, start block %llx\n",
 				page->index, squashfs_i(inode)->start);
 
+	if (!file_end) {
+		res = -EINVAL;
+		goto out;
+	}
+

file_end is computed by

	int file_end = i_size_read(inode) >> msblk->block_log;

So your "fix" will reject *any* file less than msblk->block_log in size as invalid, including perfectly valid zero size files (empty files are valid too).

[Syz log]
SQUASHFS error: Failed to read block 0x6fc: -5 SQUASHFS error: Unable to read metadata cache entry [6fa] SQUASHFS error: Unable to read metadata cache entry [6fa] SQUASHFS error: Unable to read metadata cache entry [6fa]
==================================================================

BUG: KASAN: slab-out-of-bounds in __readahead_batch include/linux/pagemap.h:1364 [inline]
BUG: KASAN: slab-out-of-bounds in squashfs_readahead+0x9a6/0x20d0 fs/squashfs/file.c:569
Write of size 8 at addr ffff88801e393648 by task syz-executor100/5067

CPU: 1 PID: 5067 Comm: syz-executor100 Not tainted 6.6.0-syzkaller-15156-g13d88ac54ddd #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
Call Trace:
  <TASK>
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
  print_address_description mm/kasan/report.c:364 [inline]
  print_report+0x163/0x540 mm/kasan/report.c:475
  kasan_report+0x142/0x170 mm/kasan/report.c:588
  __readahead_batch include/linux/pagemap.h:1364 [inline]
  squashfs_readahead+0x9a6/0x20d0 fs/squashfs/file.c:569
  read_pages+0x183/0x830 mm/readahead.c:160
  page_cache_ra_unbounded+0x68e/0x7c0 mm/readahead.c:269
  page_cache_sync_readahead include/linux/pagemap.h:1266 [inline]
  filemap_get_pages+0x49c/0x2080 mm/filemap.c:2497
  filemap_read+0x42b/0x10b0 mm/filemap.c:2593
  __kernel_read+0x425/0x8b0 fs/read_write.c:428
  integrity_kernel_read+0xb0/0xf0 security/integrity/iint.c:221
  ima_calc_file_hash_tfm security/integrity/ima/ima_crypto.c:485 [inline]
  ima_calc_file_shash security/integrity/ima/ima_crypto.c:516 [inline]
  ima_calc_file_hash+0xad1/0x1b30 security/integrity/ima/ima_crypto.c:573
  ima_collect_measurement+0x554/0xb30 security/integrity/ima/ima_api.c:290
  process_measurement+0x1373/0x21c0 security/integrity/ima/ima_main.c:359
  ima_file_check+0xf1/0x170 security/integrity/ima/ima_main.c:557
  do_open fs/namei.c:3624 [inline]
  path_openat+0x2893/0x3280 fs/namei.c:3779

[Bug]
path_openat() called open_last_lookups() before calling do_open() and open_last_lookups() will eventually call squashfs_read_inode() to set inode->i_size, but before setting i_size, it is necessary to obtain file_size from the disk.

However, during the value retrieval process, the length of the value retrieved from the disk was greater than output->length, resulting(-EIO) in the failure of squashfs_read_data(), further leading to i_size has not been initialized, i.e. its value is 0.

This resulted in the failure of squashfs_read_data(), where "SQUASHFS error:
Failed to read block 0x6fc: -5" was output in the syz log.
This also resulted in the failure of squashfs_cache_get(), outputting "SQUASHFS
error: Unable to read metadata cache entry [6fa]" in the syz log.

[Fix]
Before performing a read ahead operation in squashfs_read_folio() and squashfs_readahead(), check if i_size is not 0 before continuing.

Optimize the return value of squashfs_read_data() and return -EFBIG when the length is greater than output->length(or (index + length) > msblk->bytes_used).

Reported-and-tested-by [email protected]

Fixes f268eedddf35 ("squashfs: extend "page actor" to handle missing pages")

Signed-off-by Edward Adam Davis <[email protected]>

---
  fs/squashfs/block.c | 2 +-
  fs/squashfs/file.c  | 8 ++++++++
  2 files changed, 9 insertions(+), 1 deletion(-)

fs/squashfs/block.c +1 -1

index 581ce9519339..d335f28c822c 100644
@@ -323,7 +323,7 @@ int squashfs_read_data(struct super_block *sb, u64 index, int length,
  	}
  	if (length < 0 || length > output->length ||
  			(index + length) > msblk->bytes_used) {
-		res = -EIO;
+		res = length < 0 ? -EIO : -EFBIG;
  		goto out;
  	}
 

fs/squashfs/file.c +5 -0

index 8ba8c4c50770..5472ddd3596c 100644
@@ -461,6 +461,11 @@ static int squashfs_read_folio(struct file *file, struct folio *folio)
  	TRACE("Entered squashfs_readpage, page index %lx, start block %llx\n",
  				page->index, squashfs_i(inode)->start);
 
+	if (!file_end) {
+		res = -EINVAL;
+		goto out;
+	}
+
  	if (page->index >= ((i_size_read(inode) + PAGE_SIZE - 1) >>
  					PAGE_SHIFT))
  		goto out;

Quoted 3 lines

Reported-and-tested-by [email protected]

Fixes f268eedddf35 ("squashfs: extend "page actor" to handle missing pages")

Signed-off-by Edward Adam Davis <[email protected]>

This patch, merged to linux-next as commit 1ff947abe24a ("squashfs: fix oob in squashfs_readahead"), breaks mounting squashfs volumes on all my test systems. Let me know if you need more information to debug this issue.