[syzbot] [fs?] [mm?] kernel BUG in free_bprm

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c88416ba074a Add linux-next specific files for 20241101
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=17911630580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3ebcda5c61915e91
dashboard link: https://syzkaller.appspot.com/bug?extid=03e1af5c332f7e0eb84b
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=1626d340580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10156187980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/02f4cb9cc7aa/disk-c88416ba.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/253f54d7165b/vmlinux-c88416ba.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9f9612540588/bzImage-c88416ba.xz

The issue was bisected to:

commit 7bdc6fc85c9a1008e00e624612f82932136d7545
Author: Tycho Andersen <tand...@netflix.com>
Date: Wed Oct 30 20:37:31 2024 +0000

exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13f1aaa7980000
final oops: https://syzkaller.appspot.com/x/report.txt?x=1009aaa7980000
console output: https://syzkaller.appspot.com/x/log.txt?x=17f1aaa7980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+03e1af...@syzkaller.appspotmail.com
Fixes: 7bdc6fc85c9a ("exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case")

process 'syz-executor210' launched '/dev/fd/3' with NULL argv: empty string added
------------[ cut here ]------------
kernel BUG at arch/x86/mm/physaddr.c:23!
Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 1 UID: 0 PID: 5846 Comm: syz-executor210 Not tainted 6.12.0-rc5-next-20241101-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
RIP: 0010:__phys_addr+0x16a/0x170 arch/x86/mm/physaddr.c:23
Code: 40 a8 7a 8e 4c 89 f6 4c 89 fa e8 b1 4d aa 03 e9 45 ff ff ff e8 a7 1a 52 00 90 0f 0b e8 9f 1a 52 00 90 0f 0b e8 97 1a 52 00 90 <0f> 0b 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffc90003dd7da0 EFLAGS: 00010293
RAX: ffffffff8143a369 RBX: 000000007ffffff2 RCX: ffff88807bf53c00
RDX: 0000000000000000 RSI: 000000007ffffff2 RDI: 000000001fffffff
RBP: 1ffff1100546a409 R08: ffffffff8143a305 R09: 1ffffffff203a1f6
R10: dffffc0000000000 R11: fffffbfff203a1f7 R12: dffffc0000000000
R13: fffffffffffffff2 R14: 000000007ffffff2 R15: ffff8880760fc158
FS: 000055557e80e380(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f81836d5440 CR3: 000000002f60c000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
virt_to_folio include/linux/mm.h:1294 [inline]
kfree+0x71/0x420 mm/slub.c:4738
free_bprm+0x2b5/0x300 fs/exec.c:1499
do_execveat_common+0x3ae/0x750 fs/exec.c:1978
do_execveat fs/exec.c:2061 [inline]
__do_sys_execveat fs/exec.c:2135 [inline]
__se_sys_execveat fs/exec.c:2129 [inline]
__x64_sys_execveat+0xc4/0xe0 fs/exec.c:2129
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f432f022329
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd7487b7e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000142
RAX: ffffffffffffffda RBX: 00007ffd7487b9b8 RCX: 00007f432f022329
RDX: 0000000000000000 RSI: 0000000020000000 RDI: 0000000000000003
RBP: 00007f432f095610 R08: 0000000000001000 R09: 00007ffd7487b9b8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffd7487b9a8 R14: 0000000000000001 R15: 0000000000000001
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__phys_addr+0x16a/0x170 arch/x86/mm/physaddr.c:23
Code: 40 a8 7a 8e 4c 89 f6 4c 89 fa e8 b1 4d aa 03 e9 45 ff ff ff e8 a7 1a 52 00 90 0f 0b e8 9f 1a 52 00 90 0f 0b e8 97 1a 52 00 90 <0f> 0b 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffc90003dd7da0 EFLAGS: 00010293
RAX: ffffffff8143a369 RBX: 000000007ffffff2 RCX: ffff88807bf53c00
RDX: 0000000000000000 RSI: 000000007ffffff2 RDI: 000000001fffffff
RBP: 1ffff1100546a409 R08: ffffffff8143a305 R09: 1ffffffff203a1f6
R10: dffffc0000000000 R11: fffffbfff203a1f7 R12: dffffc0000000000
R13: fffffffffffffff2 R14: 000000007ffffff2 R15: ffff8880760fc158
FS: 000055557e80e380(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f81836d5440 CR3: 000000002f60c000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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[syzbot]

For archival purposes, forwarding an incoming command email to
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***

Subject: Re: kernel BUG in free_bprm()
Author: dman...@yandex.ru

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next 850f22c42f4b0a14a015aecc26f46f9948ded6dd

diff --git a/fs/exec.c b/fs/exec.c
index ef18eb0ea5b4..df70ed8e36fe 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1496,7 +1496,8 @@ static void free_bprm(struct linux_binprm *bprm)
if (bprm->interp != bprm->filename)
kfree(bprm->interp);
kfree(bprm->fdpath);
- kfree(bprm->argv0);
+ if (!IS_ERR(bprm->argv0))
+ kfree(bprm->argv0);
kfree(bprm);
}

[Kirill A. Shutemov]

It's better to avoid setting bprm->argv0 if strndup_user() fails.

diff --git a/fs/exec.c b/fs/exec.c
index ef18eb0ea5b4..9380e166eff5 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1504,6 +1504,7 @@ static int bprm_add_fixup_comm(struct linux_binprm *bprm,
struct user_arg_ptr argv)
{
const char __user *p = get_user_arg_ptr(argv, 0);
+ char *argv0;

/*
* If p == NULL, let's just fall back to fdpath.
@@ -1511,10 +1512,11 @@ static int bprm_add_fixup_comm(struct linux_binprm *bprm,
if (!p)
return 0;

- bprm->argv0 = strndup_user(p, MAX_ARG_STRLEN);
- if (IS_ERR(bprm->argv0))
- return PTR_ERR(bprm->argv0);
+ argv0 = strndup_user(p, MAX_ARG_STRLEN);
+ if (IS_ERR(argv0))
+ return PTR_ERR(argv0);

+ bprm->argv0 = argv0;
return 0;
}

--
Kiryl Shutsemau / Kirill A. Shutemov

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+03e1af...@syzkaller.appspotmail.com
Tested-by: syzbot+03e1af...@syzkaller.appspotmail.com

Tested on:

commit: 850f22c4 Add linux-next specific files for 20241105
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17a58f40580000
kernel config: https://syzkaller.appspot.com/x/.config?x=fa8ace328e85c186

dashboard link: https://syzkaller.appspot.com/bug?extid=03e1af5c332f7e0eb84b
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=10a5ed5f980000

Note: testing is done by a robot and is best-effort only.