general protection fault in btf_type_show

syzbot syzbot 1 participant 3 messages Aug 26 – Aug 27

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syzbot

author syzbot

2026-08-26 20:37 UTC #0 lore raw

Hello,

syzbot found the following issue on:

HEAD commit:    818bebeb63dd drm/xe: Don't hand out the flat CCS storage a..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=135ef179580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ccca94d2c01b9e78
dashboard link: https://syzkaller.appspot.com/bug?extid=37b56485bbbf90ad8489
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1437a179580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-818bebeb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6e4100526b12/vmlinux-818bebeb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/723c4783ee96/bzImage-818bebeb.xz

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

Reported-by [email protected]

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
CPU: 2 UID: 0 PID: 5908 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:btf_type_show+0x223/0x2e0 kernel/bpf/btf.c:8232
Code: c1 ea 03 80 3c 02 00 0f 85 90 00 00 00 48 8b 1c dd 40 25 fd 8b 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 77 48 8b 43 28 48 8b 0c 24 48 83 c4 08 4d 89 e9 5b
RSP: 0018:ffffc900034bf868 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000028
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: ffffc900034bf970 R11: 0000000000000001 R12: ffffffff9b96b140
R13: ffffc900034bf8e0 R14: ffff888035e3f600 R15: 0000000000000003
FS:  00005555665e7500(0000) GS:ffff8880d5da2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000000 CR3: 0000000027a0f000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 btf_type_seq_show_flags+0xca/0x120 kernel/bpf/btf.c:8250
 htab_map_seq_show_elem+0x12e/0x350 kernel/bpf/hashtab.c:1669
 map_seq_show+0x13d/0x1e0 kernel/bpf/inode.c:293
 traverse.part.0.constprop.0+0x107/0x650 fs/seq_file.c:112
 traverse fs/seq_file.c:99 [inline]
 seq_read_iter+0x93f/0x1270 fs/seq_file.c:196
 seq_read+0x344/0x4d0 fs/seq_file.c:163
 vfs_read+0x1e4/0xb40 fs/read_write.c:572
 ksys_pread64 fs/read_write.c:764 [inline]
 __do_sys_pread64 fs/read_write.c:772 [inline]
 __se_sys_pread64 fs/read_write.c:769 [inline]
 __x64_sys_pread64+0x1eb/0x250 fs/read_write.c:769
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa99f79e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff8937c6c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000011
RAX: ffffffffffffffda RBX: 00007fa99fa25fa0 RCX: 00007fa99f79e0d9
RDX: 0000000000000083 RSI: 0000200000002240 RDI: 0000000000000007
RBP: 00007fa99f835024 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000e5d6 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa99fa25fac R14: 00007fa99fa25fa0 R15: 00007fa99fa25fa0
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:btf_type_show+0x223/0x2e0 kernel/bpf/btf.c:8232
Code: c1 ea 03 80 3c 02 00 0f 85 90 00 00 00 48 8b 1c dd 40 25 fd 8b 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 77 48 8b 43 28 48 8b 0c 24 48 83 c4 08 4d 89 e9 5b
RSP: 0018:ffffc900034bf868 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000028
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: ffffc900034bf970 R11: 0000000000000001 R12: ffffffff9b96b140
R13: ffffc900034bf8e0 R14: ffff888035e3f600 R15: 0000000000000003
FS:  00005555665e7500(0000) GS:ffff8880d5da2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000000 CR3: 0000000027a0f000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
   0:	c1 ea 03             	shr    $0x3,%edx
   3:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
   7:	0f 85 90 00 00 00    	jne    0x9d
   d:	48 8b 1c dd 40 25 fd 	mov    -0x7402dac0(,%rbx,8),%rbx
  14:	8b
  15:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  1c:	fc ff df
  1f:	48 8d 7b 28          	lea    0x28(%rbx),%rdi
  23:	48 89 fa             	mov    %rdi,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2e:	75 77                	jne    0xa7
  30:	48 8b 43 28          	mov    0x28(%rbx),%rax
  34:	48 8b 0c 24          	mov    (%rsp),%rcx
  38:	48 83 c4 08          	add    $0x8,%rsp
  3c:	4d 89 e9             	mov    %r13,%r9
  3f:	5b                   	pop    %rbx

---
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syzbot

author syzbot

2026-08-26 23:38 UTC #1 lore raw

Forwarded: [PATCH] bpf: reject VAR/DATASEC as a map's BTF value type

For archival purposes, forwarding an incoming command email to [email protected], [email protected].

***

Subject: [PATCH] bpf: reject VAR/DATASEC as a map's BTF value type
Author: [email protected]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

btf_type_id_size() resolves through BTF_KIND_VAR to the size of the type it wraps, and BTF_KIND_DATASEC carries its own explicit size field. This lets map_check_btf()'s size check pass for a btf_value_type_id that points at a VAR or DATASEC, even though neither describes the memory layout of a single map value - a VAR is a named instance of a type (only meaningful inside a DATASEC), and a DATASEC is a whole ELF section of such instances.

The unresolved VAR/DATASEC id is what gets stored as map->btf_value_type_id and later handed to htab_map_seq_show_elem() -> btf_type_seq_show_flags() -> btf_type_show(), which calls btf_type_ops(t)->show() on it directly. Reject both kinds explicitly in map_check_btf() instead, right after the existing size check, so malformed BTF is rejected at BPF_MAP_CREATE time with -EINVAL.

Reported-by [email protected]

Closes https://syzkaller.appspot.com/bug?extid=37b56485bbbf90ad8489

Signed-off-by Deepanshu Kartikey <[email protected]>

---
 kernel/bpf/syscall.c | 4 ++++
 1 file changed, 4 insertions(+)

kernel/bpf/syscall.c +4 -0

index 6874ba1424af..15c4fba80cec 100644
@@ -1274,6 +1274,10 @@ static int map_check_btf(struct bpf_map *map, struct bpf_token *token,
 	if (!value_type || value_size != map->value_size)
 		return -EINVAL;
 
+	if (btf_type_is_var(value_type) ||
+            BTF_INFO_KIND(value_type->info) == BTF_KIND_DATASEC )
+		return -EINVAL;
+
 	map->record = btf_parse_fields(btf, value_type,
 				       BPF_SPIN_LOCK | BPF_RES_SPIN_LOCK | BPF_TIMER | BPF_KPTR | BPF_LIST_HEAD |
 				       BPF_RB_ROOT | BPF_REFCOUNT | BPF_WORKQUEUE | BPF_UPTR |

Signature · 1 line

2.43.0

syzbot

author syzbot

2026-08-27 01:53 UTC #2 lore raw

Forwarded: [PATCH] bpf: reject VAR/DATASEC as a map's BTF value type

In reply to syzbot

For archival purposes, forwarding an incoming command email to [email protected], [email protected].

***

Subject: [PATCH] bpf: reject VAR/DATASEC as a map's BTF value type
Author: [email protected]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Reported-by [email protected]

Closes https://syzkaller.appspot.com/bug?extid=37b56485bbbf90ad8489

Signed-off-by Deepanshu Kartikey <[email protected]>

---
 kernel/bpf/syscall.c | 4 ++++
 1 file changed, 4 insertions(+)

kernel/bpf/syscall.c +4 -0

index 6874ba1424af..15c4fba80cec 100644
@@ -1274,6 +1274,10 @@ static int map_check_btf(struct bpf_map *map, struct bpf_token *token,
 	if (!value_type || value_size != map->value_size)
 		return -EINVAL;
 
+	if (btf_type_is_var(value_type) ||
+            BTF_INFO_KIND(value_type->info) == BTF_KIND_DATASEC )
+		return -EINVAL;
+
 	map->record = btf_parse_fields(btf, value_type,
 				       BPF_SPIN_LOCK | BPF_RES_SPIN_LOCK | BPF_TIMER | BPF_KPTR | BPF_LIST_HEAD |
 				       BPF_RB_ROOT | BPF_REFCOUNT | BPF_WORKQUEUE | BPF_UPTR |

Signature · 1 line

2.43.0