memory leak in do_timer_create

syzbot New syzbot 2 participants 5 messages Nov 13, 2025 – Nov 14, 2025 Posix clocks and timers

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author syzbot

2025-11-13 04:26 UTC #0 lore raw

Hello,

syzbot found the following issue on:

HEAD commit:    24172e0d7990 Merge tag 'arm64-fixes' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=165417cd980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cb128cd5cb439809
dashboard link: https://syzkaller.appspot.com/bug?extid=9c47ad18f978d4394986
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15004914580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16ea6b42580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ded911fa4408/disk-24172e0d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a1f3e61cb784/vmlinux-24172e0d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b92fd0e25cb7/bzImage-24172e0d.xz

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

Reported-by [email protected]

2025/11/12 09:47:51 executed programs: 5

BUG: memory leak
unreferenced object 0xffff888108465800 (size 384):
  comm "syz.0.17", pid 6100, jiffies 4294944668
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace (crc 1025e73e):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4983 [inline]
    slab_alloc_node mm/slub.c:5288 [inline]
    kmem_cache_alloc_noprof+0x397/0x5a0 mm/slub.c:5295
    alloc_posix_timer kernel/time/posix-timers.c:429 [inline]
    do_timer_create+0xe0/0x800 kernel/time/posix-timers.c:478
    __do_sys_timer_create kernel/time/posix-timers.c:584 [inline]
    __se_sys_timer_create kernel/time/posix-timers.c:573 [inline]
    __x64_sys_timer_create+0xdb/0xf0 kernel/time/posix-timers.c:573
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xfa0 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff8881084a0000 (size 384):
  comm "syz.0.18", pid 6104, jiffies 4294944670
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace (crc 63c47fd0):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4983 [inline]
    slab_alloc_node mm/slub.c:5288 [inline]
    kmem_cache_alloc_noprof+0x397/0x5a0 mm/slub.c:5295
    alloc_posix_timer kernel/time/posix-timers.c:429 [inline]
    do_timer_create+0xe0/0x800 kernel/time/posix-timers.c:478
    __do_sys_timer_create kernel/time/posix-timers.c:584 [inline]
    __se_sys_timer_create kernel/time/posix-timers.c:573 [inline]
    __x64_sys_timer_create+0xdb/0xf0 kernel/time/posix-timers.c:573
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xfa0 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff8881084a0180 (size 384):
  comm "syz.0.19", pid 6107, jiffies 4294944671
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace (crc d769495f):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4983 [inline]
    slab_alloc_node mm/slub.c:5288 [inline]
    kmem_cache_alloc_noprof+0x397/0x5a0 mm/slub.c:5295
    alloc_posix_timer kernel/time/posix-timers.c:429 [inline]
    do_timer_create+0xe0/0x800 kernel/time/posix-timers.c:478
    __do_sys_timer_create kernel/time/posix-timers.c:584 [inline]
    __se_sys_timer_create kernel/time/posix-timers.c:573 [inline]
    __x64_sys_timer_create+0xdb/0xf0 kernel/time/posix-timers.c:573
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xfa0 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff888108464600 (size 384):
  comm "syz.0.20", pid 6127, jiffies 4294945201
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace (crc a3c907e):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4983 [inline]
    slab_alloc_node mm/slub.c:5288 [inline]
    kmem_cache_alloc_noprof+0x397/0x5a0 mm/slub.c:5295
    alloc_posix_timer kernel/time/posix-timers.c:429 [inline]
    do_timer_create+0xe0/0x800 kernel/time/posix-timers.c:478
    __do_sys_timer_create kernel/time/posix-timers.c:584 [inline]
    __se_sys_timer_create kernel/time/posix-timers.c:573 [inline]
    __x64_sys_timer_create+0xdb/0xf0 kernel/time/posix-timers.c:573
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xfa0 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff8881084a0300 (size 384):
  comm "syz.0.21", pid 6128, jiffies 4294945201
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace (crc bb0da4da):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4983 [inline]
    slab_alloc_node mm/slub.c:5288 [inline]
    kmem_cache_alloc_noprof+0x397/0x5a0 mm/slub.c:5295
    alloc_posix_timer kernel/time/posix-timers.c:429 [inline]
    do_timer_create+0xe0/0x800 kernel/time/posix-timers.c:478
    __do_sys_timer_create kernel/time/posix-timers.c:584 [inline]
    __se_sys_timer_create kernel/time/posix-timers.c:573 [inline]
    __x64_sys_timer_create+0xdb/0xf0 kernel/time/posix-timers.c:573
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xfa0 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

connection error: failed to recv *flatrpc.ExecutorMessageRawT: EOF

---
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syzbot

author syzbot

2025-11-14 01:20 UTC #1 lore raw

Forwarded:

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Subject:
Author: [email protected]

#syz test

syzbot

author syzbot

2025-11-14 03:54 UTC #2 lore raw

Forwarded:

In reply to syzbot

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#syz test

syzbot

author syzbot

2025-11-14 04:17 UTC #3 lore raw

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In reply to syzbot

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Subject:
Author: [email protected]

#syz test

Thomas Gleixner

2025-11-14 13:29 UTC #4 lore raw

PATCH 1/1 posix-timers: Plug a potential memory leak

In reply to syzbot

When posix timer creation is set to allocate a given timer ID and the access to the user space value faults, the function terminates without freeing the already allocated posix timer structure.

Move the allocation after the user space access to cure that.

Fixes ec2d0c04624b ("posix-timers: Provide a mechanism to allocate a given timer ID")

Reported-by [email protected]

Signed-off-by Thomas Gleixner <[email protected]>

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

---
 kernel/time/posix-timers.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

kernel/time/posix-timers.c +6 -6

@@ -475,12 +475,6 @@ static int do_timer_create(clockid_t whi
 	if (!kc->timer_create)
 		return -EOPNOTSUPP;
 
-	new_timer = alloc_posix_timer();
-	if (unlikely(!new_timer))
-		return -EAGAIN;
-
-	spin_lock_init(&new_timer->it_lock);
-
 	/* Special case for CRIU to restore timers with a given timer ID. */
 	if (unlikely(current->signal->timer_create_restore_ids)) {
 		if (copy_from_user(&req_id, created_timer_id, sizeof(req_id)))

@@ -490,6 +484,12 @@ static int do_timer_create(clockid_t whi
 			return -EINVAL;
 	}
 
+	new_timer = alloc_posix_timer();
+	if (unlikely(!new_timer))
+		return -EAGAIN;
+
+	spin_lock_init(&new_timer->it_lock);
+
 	/*
 	 * Add the timer to the hash table. The timer is not yet valid
 	 * after insertion, but has a unique ID allocated.