[syzbot] [overlayfs?] general protection fault in do_dentry_open

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8e5a478b6d6a Add linux-next specific files for 20260317
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1391d602580000
kernel config: https://syzkaller.appspot.com/x/.config?x=1d7d59e3bf573a4f
dashboard link: https://syzkaller.appspot.com/bug?extid=f34aab278bf5d664e2be
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15395b4a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=130ef8da580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d3f80068a490/disk-8e5a478b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5bfbdf243860/vmlinux-8e5a478b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f43f1bae2625/bzImage-8e5a478b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f34aab...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
CPU: 0 UID: 0 PID: 6035 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:do_dentry_open+0xaf/0x14e0 fs/open.c:896
Code: 44 24 28 80 3c 28 00 74 08 4c 89 ff e8 fa 5e ef ff 4c 89 7c 24 20 4d 89 27 4d 8d 7c 24 30 4c 89 f8 48 c1 e8 03 48 89 44 24 58 <80> 3c 28 00 74 08 4c 89 ff e8 e3 5d ef ff 4c 89 7c 24 60 4d 8b 3f
RSP: 0018:ffffc900037d7638 EFLAGS: 00010206
RAX: 0000000000000006 RBX: ffff88807217db60 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 00000000ffffffff
RBP: dffffc0000000000 R08: ffff88807b54d9b3 R09: 1ffff1100f6a9b36
R10: dffffc0000000000 R11: ffffed100f6a9b37 R12: 0000000000000000
R13: 1ffff1100e42fb7d R14: ffff88807217dbe8 R15: 0000000000000030
FS: 00005555907f6500(0000) GS:ffff888124de1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001000 CR3: 00000000772e8000 CR4: 00000000003526f0
Call Trace:
<TASK>
vfs_open+0x3b/0x340 fs/open.c:1081
backing_file_open_user_path+0x24/0x50 fs/file_table.c:73
backing_tmpfile_open+0x9b/0xf0 fs/backing-file.c:71
ovl_create_tmpfile fs/overlayfs/dir.c:1392 [inline]
ovl_tmpfile+0x400/0x810 fs/overlayfs/dir.c:1449
vfs_tmpfile+0x3ff/0x890 fs/namei.c:4744
do_tmpfile+0xd3/0x240 fs/namei.c:4809
path_openat+0x300d/0x3860 fs/namei.c:4843
do_file_open+0x23e/0x4a0 fs/namei.c:4881
do_sys_openat2+0x113/0x200 fs/open.c:1366
do_sys_open fs/open.c:1372 [inline]
__do_sys_open fs/open.c:1380 [inline]
__se_sys_open fs/open.c:1376 [inline]
__x64_sys_open+0x11e/0x150 fs/open.c:1376
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff99279c799
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:00007fff78638ef8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007ff992a15fa0 RCX: 00007ff99279c799
RDX: 0000000000000028 RSI: 0000000000551083 RDI: 0000200000000040
RBP: 00007ff992832c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff992a15fac R14: 00007ff992a15fa0 R15: 00007ff992a15fa0
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:do_dentry_open+0xaf/0x14e0 fs/open.c:896
Code: 44 24 28 80 3c 28 00 74 08 4c 89 ff e8 fa 5e ef ff 4c 89 7c 24 20 4d 89 27 4d 8d 7c 24 30 4c 89 f8 48 c1 e8 03 48 89 44 24 58 <80> 3c 28 00 74 08 4c 89 ff e8 e3 5d ef ff 4c 89 7c 24 60 4d 8b 3f
RSP: 0018:ffffc900037d7638 EFLAGS: 00010206
RAX: 0000000000000006 RBX: ffff88807217db60 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 00000000ffffffff
RBP: dffffc0000000000 R08: ffff88807b54d9b3 R09: 1ffff1100f6a9b36
R10: dffffc0000000000 R11: ffffed100f6a9b37 R12: 0000000000000000
R13: 1ffff1100e42fb7d R14: ffff88807217dbe8 R15: 0000000000000030
FS: 00005555907f6500(0000) GS:ffff888124de1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001000 CR3: 00000000772e8000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
0: 44 24 28 rex.R and $0x28,%al
3: 80 3c 28 00 cmpb $0x0,(%rax,%rbp,1)
7: 74 08 je 0x11
9: 4c 89 ff mov %r15,%rdi
c: e8 fa 5e ef ff call 0xffef5f0b
11: 4c 89 7c 24 20 mov %r15,0x20(%rsp)
16: 4d 89 27 mov %r12,(%r15)
19: 4d 8d 7c 24 30 lea 0x30(%r12),%r15
1e: 4c 89 f8 mov %r15,%rax
21: 48 c1 e8 03 shr $0x3,%rax
25: 48 89 44 24 58 mov %rax,0x58(%rsp)
* 2a: 80 3c 28 00 cmpb $0x0,(%rax,%rbp,1) <-- trapping instruction
2e: 74 08 je 0x38
30: 4c 89 ff mov %r15,%rdi
33: e8 e3 5d ef ff call 0xffef5e1b
38: 4c 89 7c 24 60 mov %r15,0x60(%rsp)
3d: 4d 8b 3f mov (%r15),%r15


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Amir Goldstein]

#syz test: https://github.com/amir73il/linux.git vfs-fixes

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to create instance: googleapi: Error 400: Invalid value for field 'resource.scheduling.preemptible': 'false'. Scheduling must have preemptible be false when OnHostMaintenance isn't TERMINATE., invalid



syzkaller build log:
go env (err=<nil>)
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE='auto'
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/syzkaller/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/syzkaller/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1926708935=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/syzkaller/jobs/linux/gopath/src/github.com/google/syzkaller/go.mod'
GOMODCACHE='/syzkaller/jobs/linux/gopath/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/syzkaller/jobs/linux/gopath'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/syzkaller/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26.0'
GOWORK=''
PKG_CONFIG='pkg-config'

git status (err=<nil>)
HEAD detached at c01bca74391
nothing to commit, working tree clean


tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
go list -f '{{.Stale}}' -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=c01bca7439117559131c7afa36f261a369581611 -X github.com/google/syzkaller/prog.gitRevisionDate=20260317-064358" ./sys/syz-sysgen | grep -q false || go install -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=c01bca7439117559131c7afa36f261a369581611 -X github.com/google/syzkaller/prog.gitRevisionDate=20260317-064358" ./sys/syz-sysgen
make .descriptions
tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
bin/syz-sysgen
touch .descriptions
GOOS=linux GOARCH=amd64 go build -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=c01bca7439117559131c7afa36f261a369581611 -X github.com/google/syzkaller/prog.gitRevisionDate=20260317-064358" -o ./bin/linux_amd64/syz-execprog github.com/google/syzkaller/tools/syz-execprog
mkdir -p ./bin/linux_amd64
g++ -o ./bin/linux_amd64/syz-executor executor/executor.cc \
-m64 -O2 -pthread -Wall -Werror -Wparentheses -Wunused-const-variable -Wframe-larger-than=16384 -Wno-stringop-overflow -Wno-array-bounds -Wno-format-overflow -Wno-unused-but-set-variable -Wno-unused-command-line-argument -static-pie -std=c++17 -I. -Iexecutor/_include -DGOOS_linux=1 -DGOARCH_amd64=1 \
-DHOSTGOOS_linux=1 -DGIT_REVISION=\"c01bca7439117559131c7afa36f261a369581611\"
/usr/bin/ld: /tmp/ccLeYWkg.o: in function `Connection::Connect(char const*, char const*)':
executor.cc:(.text._ZN10Connection7ConnectEPKcS1_[_ZN10Connection7ConnectEPKcS1_]+0x386): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
./tools/check-syzos.sh 2>/dev/null



Tested on:

commit: 045aba2b fs: allow vfs code to open an O_PATH file wit..
git tree: https://github.com/amir73il/linux.git vfs-fixes
kernel config: https://syzkaller.appspot.com/x/.config?x=6fb7e86cc0b17d78

dashboard link: https://syzkaller.appspot.com/bug?extid=f34aab278bf5d664e2be
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Note: no patches were applied.