[syzbot] [kernel?] KASAN: global-out-of-bounds Read in bus_uevent_store

[syzbot] [kernel?] KASAN: global-out-of-bounds Read in bus_uevent_store

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    50d05c7c76c9 Merge tag 'landlock-7.3-rc3' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15489c8e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=85bc5cc2fc7394d9
dashboard link: https://syzkaller.appspot.com/bug?extid=9a321aea9d851b299486
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17de9905580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11f042d1580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-50d05c7c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/303a0ade8f9e/vmlinux-50d05c7c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/70b8ca71442b/bzImage-50d05c7c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9a321aea9d851b299486@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: global-out-of-bounds in kobject_action_type lib/kobject_uevent.c:86 [inline]
BUG: KASAN: global-out-of-bounds in kobject_synth_uevent+0x79d/0x7d0 lib/kobject_uevent.c:200
Read of size 1 at addr ffffffff8d72559f by task syz.0.17/5917

CPU: 2 UID: 0 PID: 5917 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
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
 kobject_action_type lib/kobject_uevent.c:86 [inline]
 kobject_synth_uevent+0x79d/0x7d0 lib/kobject_uevent.c:200
 bus_uevent_store+0x3d/0x90 drivers/base/bus.c:917
 bus_attr_store+0x74/0xb0 drivers/base/bus.c:172
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6af/0x1050 fs/read_write.c:687
 ksys_write+0x12a/0x250 fs/read_write.c:739
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
 __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
 do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf702efec
Code: Unable to access opcode bytes at 0xf702efc2.
RSP: 002b:00000000ffa3eb5c EFLAGS: 00000296 ORIG_RAX: 0000000000000004
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000080000280
RDX: 000000000000ff0a RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

The buggy address belongs to the variable:
 kobject_actions+0xdff/0x4e80

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xd725
flags: 0xfff00000002000(reserved|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000002000 ffffea000035c948 ffffea000035c948 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)

Memory state around the buggy address:
 ffffffff8d725480: f9 f9 f9 f9 00 06 f9 f9 f9 f9 f9 f9 00 06 f9 f9
 ffffffff8d725500: f9 f9 f9 f9 00 00 01 f9 f9 f9 f9 f9 00 00 02 f9
>ffffffff8d725580: f9 f9 f9 f9 00 06 f9 f9 f9 f9 f9 f9 00 07 f9 f9
                            ^
 ffffffff8d725600: f9 f9 f9 f9 00 00 06 f9 f9 f9 f9 f9 00 04 f9 f9
 ffffffff8d725680: f9 f9 f9 f9 00 06 f9 f9 f9 f9 f9 f9 00 05 f9 f9
==================================================================


---
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Re: [syzbot] [kernel?] KASAN: global-out-of-bounds Read in bus_uevent_store

[Edward Adam Davis]

From: Edward Aadm Davis <eadavis@sina.com>

#syz test: upstream 50d05c7c76c9

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index ddbc4d7482d2..25c89a36fb39 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -83,7 +83,8 @@ static int kobject_action_type(const char *buf, size_t count,
 	for (action = 0; action < ARRAY_SIZE(kobject_actions); action++) {
 		if (strncmp(kobject_actions[action], buf, count_first) != 0)
 			continue;
-		if (kobject_actions[action][count_first] != '\0')
+		if (count_first <= strlen(kobject_actions[action]) &&
+		    kobject_actions[action][count_first] != '\0')
 			continue;
 		if (args)
 			*args = args_start;

Re: [syzbot] [kernel?] KASAN: global-out-of-bounds Read in bus_uevent_store

[syzbot]

Hello,

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

Reported-by: syzbot+9a321aea9d851b299486@syzkaller.appspotmail.com
Tested-by: syzbot+9a321aea9d851b299486@syzkaller.appspotmail.com

Tested on:

commit:         50d05c7c Merge tag 'landlock-7.3-rc3' of git://git.ker..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1030fdf9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=85bc5cc2fc7394d9
dashboard link: https://syzkaller.appspot.com/bug?extid=9a321aea9d851b299486
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
userspace arch: i386
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13c07905580000

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

Re: [syzbot] [kernel?] KASAN: global-out-of-bounds Read in bus_uevent_store

[Edward Adam Davis]

From: Edward Aadm Davis <eadavis@sina.com>

#syz test: upstream 50d05c7c76c9

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index cd5bb0f9fee6..a63130d18680 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -228,10 +228,12 @@ static const struct kernfs_ops sysfs_file_kfops_ro = {
 };
 
 static const struct kernfs_ops sysfs_file_kfops_wo = {
+	.atomic_write_len	= PAGE_SIZE,
 	.write		= sysfs_kf_write,
 };
 
 static const struct kernfs_ops sysfs_file_kfops_rw = {
+	.atomic_write_len	= PAGE_SIZE,
 	.seq_show	= sysfs_kf_seq_show,
 	.write		= sysfs_kf_write,
 };

Re: [syzbot] [kernel?] KASAN: global-out-of-bounds Read in bus_uevent_store

[syzbot]

Hello,

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

Reported-by: syzbot+9a321aea9d851b299486@syzkaller.appspotmail.com
Tested-by: syzbot+9a321aea9d851b299486@syzkaller.appspotmail.com

Tested on:

commit:         50d05c7c Merge tag 'landlock-7.3-rc3' of git://git.ker..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=14307905580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=85bc5cc2fc7394d9
dashboard link: https://syzkaller.appspot.com/bug?extid=9a321aea9d851b299486
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
userspace arch: i386
patch:          https://syzkaller.appspot.com/x/patch.diff?x=147348c9580000

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

[PATCH] sysfs: prevent writing excessively large files

[Edward Adam Davis]

Since atomic_write_len is not configured for sysfs_file_kfops_rw, a large
file write via sysfs_kf_write() may result in an out-of-bounds read when
checking for the null terminator of a string element in the kobject_actions
array within kobject_action_type(), potentially hitting:

BUG: KASAN: global-out-of-bounds in kobject_action_type lib/kobject_uevent.c:86 [inline]
BUG: KASAN: global-out-of-bounds in kobject_synth_uevent+0x79d/0x7d0 lib/kobject_uevent.c:200
Read of size 1 at addr ffffffff8d72559f by task syz.0.17/5917
Call Trace:
 kobject_action_type lib/kobject_uevent.c:86 [inline]
 kobject_synth_uevent+0x79d/0x7d0 lib/kobject_uevent.c:200
 bus_uevent_store+0x3d/0x90 drivers/base/bus.c:917
 bus_attr_store+0x74/0xb0 drivers/base/bus.c:172
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
 kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6af/0x1050 fs/read_write.c:687

Add atomic_write_len for sysfs_file_kfops_rw and sysfs_file_kfops_wo
properly.

Fixes: f6acf8bb6a40 ("sysfs, kernfs: introduce kernfs_ops")
Reported-by: syzbot+9a321aea9d851b299486@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9a321aea9d851b299486
Tested-by: syzbot+9a321aea9d851b299486@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@sina.com>
---
 fs/sysfs/file.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index cd5bb0f9fee6..a63130d18680 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -228,10 +228,12 @@ static const struct kernfs_ops sysfs_file_kfops_ro = {
 };
 
 static const struct kernfs_ops sysfs_file_kfops_wo = {
+	.atomic_write_len	= PAGE_SIZE,
 	.write		= sysfs_kf_write,
 };
 
 static const struct kernfs_ops sysfs_file_kfops_rw = {
+	.atomic_write_len	= PAGE_SIZE,
 	.seq_show	= sysfs_kf_seq_show,
 	.write		= sysfs_kf_write,
 };
-- 
2.43.0

Re: [PATCH] sysfs: prevent writing excessively large files

[Greg KH]

On Tue, Sep 15, 2026 at 08:20:17PM +0800, Edward Adam Davis wrote:
> Since atomic_write_len is not configured for sysfs_file_kfops_rw, a large
> file write via sysfs_kf_write() may result in an out-of-bounds read when
> checking for the null terminator of a string element in the kobject_actions
> array within kobject_action_type(), potentially hitting:

What sysfs file are you hitting this on?

> 
> BUG: KASAN: global-out-of-bounds in kobject_action_type lib/kobject_uevent.c:86 [inline]
> BUG: KASAN: global-out-of-bounds in kobject_synth_uevent+0x79d/0x7d0 lib/kobject_uevent.c:200
> Read of size 1 at addr ffffffff8d72559f by task syz.0.17/5917
> Call Trace:
>  kobject_action_type lib/kobject_uevent.c:86 [inline]
>  kobject_synth_uevent+0x79d/0x7d0 lib/kobject_uevent.c:200
>  bus_uevent_store+0x3d/0x90 drivers/base/bus.c:917
>  bus_attr_store+0x74/0xb0 drivers/base/bus.c:172
>  sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
>  kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
>  new_sync_write fs/read_write.c:595 [inline]
>  vfs_write+0x6af/0x1050 fs/read_write.c:687
> 
> Add atomic_write_len for sysfs_file_kfops_rw and sysfs_file_kfops_wo
> properly.
> 
> Fixes: f6acf8bb6a40 ("sysfs, kernfs: introduce kernfs_ops")

What changed to suddenly cause this to show up now if this has been
present for decades?

thanks,

greg k-h

Re: [PATCH] sysfs: prevent writing excessively large files

[Edward Adam Davis]

From: Edward Aadm Davis <eadavis@sina.com>

On Wed, 16 Sep 2026 09:17:56 +0200, Greg KH wrote:
> > Since atomic_write_len is not configured for sysfs_file_kfops_rw, a large
> > file write via sysfs_kf_write() may result in an out-of-bounds read when
> > checking for the null terminator of a string element in the kobject_actions
> > array within kobject_action_type(), potentially hitting:
> 
> What sysfs file are you hitting this on?
Regular sysfs files.
> 
> >
> > BUG: KASAN: global-out-of-bounds in kobject_action_type lib/kobject_uevent.c:86 [inline]
> > BUG: KASAN: global-out-of-bounds in kobject_synth_uevent+0x79d/0x7d0 lib/kobject_uevent.c:200
> > Read of size 1 at addr ffffffff8d72559f by task syz.0.17/5917
> > Call Trace:
> >  kobject_action_type lib/kobject_uevent.c:86 [inline]
> >  kobject_synth_uevent+0x79d/0x7d0 lib/kobject_uevent.c:200
> >  bus_uevent_store+0x3d/0x90 drivers/base/bus.c:917
> >  bus_attr_store+0x74/0xb0 drivers/base/bus.c:172
> >  sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
> >  kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
> >  new_sync_write fs/read_write.c:595 [inline]
> >  vfs_write+0x6af/0x1050 fs/read_write.c:687
> >
> > Add atomic_write_len for sysfs_file_kfops_rw and sysfs_file_kfops_wo
> > properly.
> >
> > Fixes: f6acf8bb6a40 ("sysfs, kernfs: introduce kernfs_ops")
> 
> What changed to suddenly cause this to show up now if this has been
> present for decades?
This issue has always existed. It remained undetected simply because the
buffer lengths typically passed when writing to `/sys/bus/acpi/uevent`
happened to be reasonably appropriate.

cheers,
Edward