[syzbot] [ntfs3?] KMSAN: uninit-value in attr_set_size

[syzbot] [ntfs3?] KMSAN: uninit-value in attr_set_size

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    9b0d551bcc05 Merge tag 'pull-misc' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11da692f980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=50fb29d81ff5a3df
dashboard link: https://syzkaller.appspot.com/bug?extid=83c9dd5c0dcf6184fdbf
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=143915cd980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13dbd334580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/90b0fb888152/disk-9b0d551b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1120c646f284/vmlinux-9b0d551b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/df9bbfa8cbe6/bzImage-9b0d551b.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/0277c876bf11/mount_8.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+83c9dd5c0dcf6184fdbf@syzkaller.appspotmail.com

ntfs3(loop0): Failed to initialize $Extend.
=====================================================
BUG: KMSAN: uninit-value in attr_set_size+0x471b/0x6740 fs/ntfs3/attrib.c:653
 attr_set_size+0x471b/0x6740 fs/ntfs3/attrib.c:653
 ntfs_set_size+0x222/0x330 fs/ntfs3/inode.c:861
 ntfs_extend+0x27c/0xf50 fs/ntfs3/file.c:359
 ntfs_file_write_iter+0x627/0x10d0 fs/ntfs3/file.c:1220
 iter_file_splice_write+0x12b2/0x2170 fs/splice.c:738
 ntfs_file_splice_write+0x21d/0x370 fs/ntfs3/file.c:1347
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x317/0x7d0 fs/splice.c:1161
 splice_direct_to_actor+0x99f/0x1550 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x1e0/0x350 fs/splice.c:1230
 do_sendfile+0x9eb/0x1110 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64+0x1e3/0x280 fs/read_write.c:1417
 __x64_sys_sendfile64+0xbd/0x120 fs/read_write.c:1417
 x64_sys_call+0x36b8/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
 attr_set_size+0x4714/0x6740 fs/ntfs3/attrib.c:655
 ntfs_set_size+0x222/0x330 fs/ntfs3/inode.c:861
 ntfs_extend+0x27c/0xf50 fs/ntfs3/file.c:359
 ntfs_file_write_iter+0x627/0x10d0 fs/ntfs3/file.c:1220
 iter_file_splice_write+0x12b2/0x2170 fs/splice.c:738
 ntfs_file_splice_write+0x21d/0x370 fs/ntfs3/file.c:1347
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x317/0x7d0 fs/splice.c:1161
 splice_direct_to_actor+0x99f/0x1550 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x1e0/0x350 fs/splice.c:1230
 do_sendfile+0x9eb/0x1110 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64+0x1e3/0x280 fs/read_write.c:1417
 __x64_sys_sendfile64+0xbd/0x120 fs/read_write.c:1417
 x64_sys_call+0x36b8/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
 ni_create_attr_list+0x1b9b/0x1db0 fs/ntfs3/frecord.c:872
 attr_set_size+0x4174/0x6740 fs/ntfs3/attrib.c:640
 ntfs_set_size+0x222/0x330 fs/ntfs3/inode.c:861
 ntfs_extend+0x27c/0xf50 fs/ntfs3/file.c:359
 ntfs_file_write_iter+0x627/0x10d0 fs/ntfs3/file.c:1220
 iter_file_splice_write+0x12b2/0x2170 fs/splice.c:738
 ntfs_file_splice_write+0x21d/0x370 fs/ntfs3/file.c:1347
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x317/0x7d0 fs/splice.c:1161
 splice_direct_to_actor+0x99f/0x1550 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x1e0/0x350 fs/splice.c:1230
 do_sendfile+0x9eb/0x1110 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64+0x1e3/0x280 fs/read_write.c:1417
 __x64_sys_sendfile64+0xbd/0x120 fs/read_write.c:1417
 x64_sys_call+0x36b8/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
 slab_post_alloc_hook mm/slub.c:4953 [inline]
 slab_alloc_node mm/slub.c:5245 [inline]
 __do_kmalloc_node mm/slub.c:5602 [inline]
 __kmalloc_noprof+0xabb/0x1b40 mm/slub.c:5615
 kmalloc_noprof include/linux/slab.h:961 [inline]
 ni_create_attr_list+0x1ca/0x1db0 fs/ntfs3/frecord.c:770
 attr_set_size+0x4174/0x6740 fs/ntfs3/attrib.c:640
 ntfs_set_size+0x222/0x330 fs/ntfs3/inode.c:861
 ntfs_extend+0x27c/0xf50 fs/ntfs3/file.c:359
 ntfs_file_write_iter+0x627/0x10d0 fs/ntfs3/file.c:1220
 iter_file_splice_write+0x12b2/0x2170 fs/splice.c:738
 ntfs_file_splice_write+0x21d/0x370 fs/ntfs3/file.c:1347
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x317/0x7d0 fs/splice.c:1161
 splice_direct_to_actor+0x99f/0x1550 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x1e0/0x350 fs/splice.c:1230
 do_sendfile+0x9eb/0x1110 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64+0x1e3/0x280 fs/read_write.c:1417
 __x64_sys_sendfile64+0xbd/0x120 fs/read_write.c:1417
 x64_sys_call+0x36b8/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 6199 Comm: syz.0.54 Not tainted syzkaller #0 PREEMPT(none) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
=====================================================


---
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[PATCH] fs/ntfs3: fix KMSAN uninit-value in ni_create_attr_list

[Nirbhay Sharma]

The call to kmalloc() to allocate the attribute list buffer is given a
size of al_aligned(rs). This size can be larger than the data
subsequently copied into the buffer, leaving trailing bytes uninitialized.

This can trigger a KMSAN "uninit-value" warning if that memory is
later accessed.

Fix this by using kzalloc() instead, which ensures the entire
allocated buffer is zero-initialized, preventing the warning.

Reported-by: syzbot+83c9dd5c0dcf6184fdbf@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=83c9dd5c0dcf6184fdbf
Signed-off-by: Nirbhay Sharma <nirbhay.lkd@gmail.com>
---
The following syzbot test commands were used to verify the fix against
both linux-next and a specific mainline commit. Both kernels were
configured with CONFIG_KMSAN=y, and no KMSAN warnings were observed
with the patch applied.

An attempt to test against the latest mainline tip failed due to an
unrelated boot failure in the SCSI subsystem (KMSAN: use-after-free in
scsi_get_vpd_buf). Therefore, testing was done on the last known-good
mainline commit below.

For mainline commit 9b0d551bcc05 ("Merge tag 'pull-misc' of..."):
#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 9b0d551bcc05

For the linux-next branch:
#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master

 fs/ntfs3/frecord.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ntfs3/frecord.c b/fs/ntfs3/frecord.c
index 8f9fe1d7a690..4fe8da7fc034 100644
--- a/fs/ntfs3/frecord.c
+++ b/fs/ntfs3/frecord.c
@@ -767,7 +767,7 @@ int ni_create_attr_list(struct ntfs_inode *ni)
 	 * Skip estimating exact memory requirement.
 	 * Looks like one record_size is always enough.
 	 */
-	le = kmalloc(al_aligned(rs), GFP_NOFS);
+	le = kzalloc(al_aligned(rs), GFP_NOFS);
 	if (!le)
 		return -ENOMEM;
 
-- 
2.51.0

Re: [syzbot] [ntfs3?] KMSAN: uninit-value in attr_set_size

[syzbot]

Hello,

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

Reported-by: syzbot+83c9dd5c0dcf6184fdbf@syzkaller.appspotmail.com
Tested-by: syzbot+83c9dd5c0dcf6184fdbf@syzkaller.appspotmail.com

Tested on:

commit:         9b0d551b Merge tag 'pull-misc' of git://git.kernel.org..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=17a855cd980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=50fb29d81ff5a3df
dashboard link: https://syzkaller.appspot.com/bug?extid=83c9dd5c0dcf6184fdbf
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1609f942580000

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

Re: [PATCH] fs/ntfs3: fix KMSAN uninit-value in ni_create_attr_list

[Nirbhay Sharma]

On 10/7/25 4:08 AM, Nirbhay Sharma wrote:
> The call to kmalloc() to allocate the attribute list buffer is given a
> size of al_aligned(rs). This size can be larger than the data
> subsequently copied into the buffer, leaving trailing bytes uninitialized.
> 
> This can trigger a KMSAN "uninit-value" warning if that memory is
> later accessed.
> 
> Fix this by using kzalloc() instead, which ensures the entire
> allocated buffer is zero-initialized, preventing the warning.
> 
> Reported-by: syzbot+83c9dd5c0dcf6184fdbf@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=83c9dd5c0dcf6184fdbf
> Signed-off-by: Nirbhay Sharma <nirbhay.lkd@gmail.com>
> ---
> The following syzbot test commands were used to verify the fix against
> both linux-next and a specific mainline commit. Both kernels were
> configured with CONFIG_KMSAN=y, and no KMSAN warnings were observed
> with the patch applied.
> 
> An attempt to test against the latest mainline tip failed due to an
> unrelated boot failure in the SCSI subsystem (KMSAN: use-after-free in
> scsi_get_vpd_buf). Therefore, testing was done on the last known-good
> mainline commit below.
> 
> For mainline commit 9b0d551bcc05 ("Merge tag 'pull-misc' of..."):
> #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 9b0d551bcc05
> 
> For the linux-next branch:
> #syz test: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> 
>   fs/ntfs3/frecord.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ntfs3/frecord.c b/fs/ntfs3/frecord.c
> index 8f9fe1d7a690..4fe8da7fc034 100644
> --- a/fs/ntfs3/frecord.c
> +++ b/fs/ntfs3/frecord.c
> @@ -767,7 +767,7 @@ int ni_create_attr_list(struct ntfs_inode *ni)
>   	 * Skip estimating exact memory requirement.
>   	 * Looks like one record_size is always enough.
>   	 */
> -	le = kmalloc(al_aligned(rs), GFP_NOFS);
> +	le = kzalloc(al_aligned(rs), GFP_NOFS);
>   	if (!le)
>   		return -ENOMEM;
>   
Hi Konstantin,

I sent this patch about 3 weeks ago and haven't heard back yet. I wanted
to check if there are any concerns with the patch or if any changes are
needed. The fix addresses a KMSAN uninit-value bug and has been tested
successfully on both linux-next and the commit from the syzbot report.

Please let me know if you need any additional information or testing.

Thanks,
Nirbhay

Re: [PATCH] fs/ntfs3: fix KMSAN uninit-value in ni_create_attr_list

[Konstantin Komarov]

On 10/25/25 17:07, Nirbhay Sharma wrote:
>
>
> On 10/7/25 4:08 AM, Nirbhay Sharma wrote:
>> The call to kmalloc() to allocate the attribute list buffer is given a
>> size of al_aligned(rs). This size can be larger than the data
>> subsequently copied into the buffer, leaving trailing bytes 
>> uninitialized.
>>
>> This can trigger a KMSAN "uninit-value" warning if that memory is
>> later accessed.
>>
>> Fix this by using kzalloc() instead, which ensures the entire
>> allocated buffer is zero-initialized, preventing the warning.
>>
>> Reported-by: syzbot+83c9dd5c0dcf6184fdbf@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=83c9dd5c0dcf6184fdbf
>> Signed-off-by: Nirbhay Sharma <nirbhay.lkd@gmail.com>
>> ---
>> The following syzbot test commands were used to verify the fix against
>> both linux-next and a specific mainline commit. Both kernels were
>> configured with CONFIG_KMSAN=y, and no KMSAN warnings were observed
>> with the patch applied.
>>
>> An attempt to test against the latest mainline tip failed due to an
>> unrelated boot failure in the SCSI subsystem (KMSAN: use-after-free in
>> scsi_get_vpd_buf). Therefore, testing was done on the last known-good
>> mainline commit below.
>>
>> For mainline commit 9b0d551bcc05 ("Merge tag 'pull-misc' of..."):
>> #syz test: 
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 
>> 9b0d551bcc05
>>
>> For the linux-next branch:
>> #syz test: 
>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 
>> master
>>
>>   fs/ntfs3/frecord.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/ntfs3/frecord.c b/fs/ntfs3/frecord.c
>> index 8f9fe1d7a690..4fe8da7fc034 100644
>> --- a/fs/ntfs3/frecord.c
>> +++ b/fs/ntfs3/frecord.c
>> @@ -767,7 +767,7 @@ int ni_create_attr_list(struct ntfs_inode *ni)
>>        * Skip estimating exact memory requirement.
>>        * Looks like one record_size is always enough.
>>        */
>> -    le = kmalloc(al_aligned(rs), GFP_NOFS);
>> +    le = kzalloc(al_aligned(rs), GFP_NOFS);
>>       if (!le)
>>           return -ENOMEM;
> Hi Konstantin,
>
> I sent this patch about 3 weeks ago and haven't heard back yet. I wanted
> to check if there are any concerns with the patch or if any changes are
> needed. The fix addresses a KMSAN uninit-value bug and has been tested
> successfully on both linux-next and the commit from the syzbot report.
>
> Please let me know if you need any additional information or testing.
>
> Thanks,
> Nirbhay

Hello,

Your patch has been applied, but it hasn’t been pushed to our repository
yet. It will be there as soon as possible.

I’ll let you know once it’s merged into kernel. Thanks for your patience.

Regards,
Konstantin