[syzbot] [hfs?] kernel BUG in hfsplus_show_options

[syzbot] [hfs?] kernel BUG in hfsplus_show_options

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    aeba456828b4 Add linux-next specific files for 20230718
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=111d6a62a80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e7ec534f91cfce6c
dashboard link: https://syzkaller.appspot.com/bug?extid=98d3ceb7e01269e7bf4f
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15ecf646a80000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1476f30aa80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/94f67a948e1d/disk-aeba4568.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9818a252eddd/vmlinux-aeba4568.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fbf9befe9bc9/bzImage-aeba4568.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/d8265d21ad1c/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+98d3ceb7e01269e7bf4f@syzkaller.appspotmail.com

memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL, pid=5032 'syz-executor324'
loop0: detected capacity change from 0 to 1024
detected buffer overflow in strnlen
------------[ cut here ]------------
kernel BUG at lib/string_helpers.c:1031!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 5032 Comm: syz-executor324 Not tainted 6.5.0-rc2-next-20230718-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/03/2023
RIP: 0010:fortify_panic+0x1c/0x20 lib/string_helpers.c:1031
Code: ba fd eb d7 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 53 48 89 fb e8 23 de 65 fd 48 89 de 48 c7 c7 00 2c c8 8a e8 e4 28 49 fd <0f> 0b 66 90 f3 0f 1e fa 41 55 41 54 55 53 48 89 fb e8 fe dd 65 fd
RSP: 0018:ffffc90003a1f7b8 EFLAGS: 00010282
RAX: 0000000000000023 RBX: ffffffff8a873580 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff816aad20 RDI: 0000000000000005
RBP: ffff888019f16cb8 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000080000000 R11: 0000000000000001 R12: 1ffff92000743efa
R13: 0000000000000004 R14: ffff888078fa69c0 R15: ffffc90003a1f7f0
FS:  0000555556e72380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000456b30 CR3: 0000000079883000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 strnlen include/linux/fortify-string.h:181 [inline]
 strscpy include/linux/fortify-string.h:324 [inline]
 hfsplus_show_options+0x658/0x740 fs/hfsplus/options.c:226
 show_mountinfo+0x671/0x990 fs/proc_namespace.c:191
 seq_read_iter+0xaf0/0x1280 fs/seq_file.c:272
 call_read_iter include/linux/fs.h:1911 [inline]
 copy_splice_read+0x418/0x8f0 fs/splice.c:366
 vfs_splice_read fs/splice.c:993 [inline]
 vfs_splice_read+0x2c8/0x3b0 fs/splice.c:962
 splice_direct_to_actor+0x2a5/0xa30 fs/splice.c:1069
 do_splice_direct+0x1af/0x280 fs/splice.c:1194
 do_sendfile+0xb88/0x1390 fs/read_write.c:1254
 __do_sys_sendfile64 fs/read_write.c:1322 [inline]
 __se_sys_sendfile64 fs/read_write.c:1308 [inline]
 __x64_sys_sendfile64+0x1d6/0x220 fs/read_write.c:1308
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f4339573a79
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:00007ffff9271428 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007ffff9271430 RCX: 00007f4339573a79
RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000004
RBP: 00007f43395e7610 R08: 0000000000000000 R09: 65732f636f72702f
R10: 0800000080004105 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffff9271668 R14: 0000000000000001 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:fortify_panic+0x1c/0x20 lib/string_helpers.c:1031
Code: ba fd eb d7 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 53 48 89 fb e8 23 de 65 fd 48 89 de 48 c7 c7 00 2c c8 8a e8 e4 28 49 fd <0f> 0b 66 90 f3 0f 1e fa 41 55 41 54 55 53 48 89 fb e8 fe dd 65 fd
RSP: 0018:ffffc90003a1f7b8 EFLAGS: 00010282
RAX: 0000000000000023 RBX: ffffffff8a873580 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff816aad20 RDI: 0000000000000005
RBP: ffff888019f16cb8 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000080000000 R11: 0000000000000001 R12: 1ffff92000743efa
R13: 0000000000000004 R14: ffff888078fa69c0 R15: ffffc90003a1f7f0
FS:  0000555556e72380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000456b30 CR3: 0000000079883000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
This report is generated by a bot. It may contain errors.
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If the bug is already fixed, let syzbot know by replying with:
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If you want syzbot to run the reproducer, reply with:
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Re: [syzbot] [hfs?] kernel BUG in hfsplus_show_options

[syzbot]

syzbot has bisected this issue to:

commit c30417b20f4993e49406f3f6d986355c6e943aa2
Author: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Date:   Mon Jul 17 09:33:32 2023 +0000

    seq_file: Replace strncpy()+nul by strscpy()

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17488c1aa80000
start commit:   aeba456828b4 Add linux-next specific files for 20230718
git tree:       linux-next
final oops:     https://syzkaller.appspot.com/x/report.txt?x=14c88c1aa80000
console output: https://syzkaller.appspot.com/x/log.txt?x=10c88c1aa80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e7ec534f91cfce6c
dashboard link: https://syzkaller.appspot.com/bug?extid=98d3ceb7e01269e7bf4f
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15ecf646a80000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1476f30aa80000

Reported-by: syzbot+98d3ceb7e01269e7bf4f@syzkaller.appspotmail.com
Fixes: c30417b20f49 ("seq_file: Replace strncpy()+nul by strscpy()")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] [hfs?] kernel BUG in hfsplus_show_options

[Kees Cook]

On July 18, 2023 6:27:23 PM PDT, syzbot <syzbot+98d3ceb7e01269e7bf4f@syzkaller.appspotmail.com> wrote:
>syzbot has bisected this issue to:
>
>commit c30417b20f4993e49406f3f6d986355c6e943aa2
>Author: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>Date:   Mon Jul 17 09:33:32 2023 +0000
>
>    seq_file: Replace strncpy()+nul by strscpy()

Uh... Wat. Is this a bug in strscpy fortification? It's copying out of a (recast) be32... It shouldn't expect to find a NUL because it hit the max copy size already...

Looking...

-Kees

>
>bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17488c1aa80000
>start commit:   aeba456828b4 Add linux-next specific files for 20230718
>git tree:       linux-next
>final oops:     https://syzkaller.appspot.com/x/report.txt?x=14c88c1aa80000
>console output: https://syzkaller.appspot.com/x/log.txt?x=10c88c1aa80000
>kernel config:  https://syzkaller.appspot.com/x/.config?x=e7ec534f91cfce6c
>dashboard link: https://syzkaller.appspot.com/bug?extid=98d3ceb7e01269e7bf4f
>syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15ecf646a80000
>C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1476f30aa80000
>
>Reported-by: syzbot+98d3ceb7e01269e7bf4f@syzkaller.appspotmail.com
>Fixes: c30417b20f49 ("seq_file: Replace strncpy()+nul by strscpy()")
>
>For information about bisection process see: https://goo.gl/tpsmEJ#bisection


-- 
Kees Cook

[PATCH] fortify: strnlen: Call fortify_panic() only if the number of bytes read is greater than maxlen

[sel4]

From: Brandon Luo <sel4@tilde.club>

If the number of bytes read is p_size and p_size is less than maxlen,
fortify_panic() will be called incorrectly. Only panic if the number of
bytes read is greater than the minimum of p_size and maxlen since that is
 the argument to __real_strnlen().

Reported-by: syzbot+98d3ceb7e01269e7bf4f@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000d8352e0600c0c804@google.com/

Reported-by: syzbot+155274e882dcbf9885df@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000de4c2c0600c02b28@google.com/

Signed-off-by: Brandon Luo <sel4@tilde.club>
---
 include/linux/fortify-string.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index da51a83b2829..cde637f735fe 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -176,8 +176,9 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size
 	}
 
 	/* Do not check characters beyond the end of p. */
-	ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
-	if (p_size <= ret && maxlen != ret)
+	maxlen = (maxlen < p_size) ? maxlen : p_size;
+	ret = __real_strnlen(p, maxlen);
+	if (maxlen < ret)
 		fortify_panic(__func__);
 	return ret;
 }
-- 
2.41.0

Re: [PATCH] fortify: strnlen: Call fortify_panic() only if the number of bytes read is greater than maxlen

[Kees Cook]

On July 24, 2023 3:48:57 PM PDT, sel4@tilde.club wrote:
>From: Brandon Luo <sel4@tilde.club>
>
>If the number of bytes read is p_size and p_size is less than maxlen,
>fortify_panic() will be called incorrectly. Only panic if the number of
>bytes read is greater than the minimum of p_size and maxlen since that is
> the argument to __real_strnlen().
>
>Reported-by: syzbot+98d3ceb7e01269e7bf4f@syzkaller.appspotmail.com
>Closes: https://lore.kernel.org/all/000000000000d8352e0600c0c804@google.com/
>
>Reported-by: syzbot+155274e882dcbf9885df@syzkaller.appspotmail.com
>Closes: https://lore.kernel.org/all/000000000000de4c2c0600c02b28@google.com/

Thanks for looking at these, but strnlen is working correctly. The problem was hfs's overread of a cast be32 when used with strscpy. See:
https://lore.kernel.org/lkml/202307182147.A5B81B67D@keescook/

-Kees

>
>Signed-off-by: Brandon Luo <sel4@tilde.club>
>---
> include/linux/fortify-string.h | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
>diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
>index da51a83b2829..cde637f735fe 100644
>--- a/include/linux/fortify-string.h
>+++ b/include/linux/fortify-string.h
>@@ -176,8 +176,9 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size
> 	}
> 
> 	/* Do not check characters beyond the end of p. */
>-	ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
>-	if (p_size <= ret && maxlen != ret)
>+	maxlen = (maxlen < p_size) ? maxlen : p_size;
>+	ret = __real_strnlen(p, maxlen);
>+	if (maxlen < ret)
> 		fortify_panic(__func__);
> 	return ret;
> }


-- 
Kees Cook

Re: [syzbot] [hfs?] kernel BUG in hfsplus_show_options

[syzbot]

Hello,

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

failed to apply patch:
checking file include/linux/fortify-string.h
patch: **** unexpected end of file in patch



Tested on:

commit:         aeba4568 Add linux-next specific files for 20230718
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
dashboard link: https://syzkaller.appspot.com/bug?extid=98d3ceb7e01269e7bf4f
compiler:       
patch:          https://syzkaller.appspot.com/x/patch.diff?x=123c341aa80000

Re: [syzbot] [hfs?] kernel BUG in hfsplus_show_options

[syzbot]

Hello,

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

failed to apply patch:
checking file include/linux/fortify-string.h
patch: **** unexpected end of file in patch



Tested on:

commit:         aeba4568 Add linux-next specific files for 20230718
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
dashboard link: https://syzkaller.appspot.com/bug?extid=98d3ceb7e01269e7bf4f
compiler:       
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10bbdd92a80000

Re: [syzbot] [hfs?] kernel BUG in hfsplus_show_options

[syzbot]

Hello,

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

Reported-and-tested-by: syzbot+98d3ceb7e01269e7bf4f@syzkaller.appspotmail.com

Tested on:

commit:         aeba4568 Add linux-next specific files for 20230718
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=14ccebe4a80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e7ec534f91cfce6c
dashboard link: https://syzkaller.appspot.com/bug?extid=98d3ceb7e01269e7bf4f
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=144204aea80000

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