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Wed, 16 Oct 2024 07:12:55 -0700 (PDT) MIME-Version: 1.0 References: <20240922080838.15184-1-aha310510@gmail.com> In-Reply-To: <20240922080838.15184-1-aha310510@gmail.com> From: Jeongjun Park Date: Wed, 16 Oct 2024 23:12:43 +0900 Message-ID: Subject: Re: [PATCH RESEND] mm: shmem: fix data-race in shmem_getattr() To: akpm@linux-foundation.org, hughd@google.com Cc: yuzhao@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot , stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 3FD4D180012 X-Stat-Signature: cryrzgp1sc8mt4s3ekfjfp4h7zpdr4ba X-HE-Tag: 1729087967-720298 X-HE-Meta: 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 mRSFjYyM raxCpfVA/yJXfXv613wxU+P3EOLeaBJP2e/Q+80CmoxnZZLbBVHfHMD7AErNa4pwolyDcy0znpXTK74G5oCbhkmugLgoMrr8gzu48g8+roJqRJuO5hybTnRhsNkHImF/XGG+v+BU3nabQBPILxUB4NfZNQZcgkllZL+6nSKQz3JLiqQmG2illSwSIKOl5WpEretY0oinh7stJJBhph5+AxsuG2kFzYL4pgVSvAXzPi9ZRRk8yPPSiqCD2nqI9+aID7k8CiXtXiH1V4QYkXyYpjnBvwPvEk/33+CvJW5N2S9sp5ui6fBp8smmjlPToRFT6ttr7rD3pSO5yTOsOyiK0tG9/bP2mq46cMOgP3rs2Ph47hbYukKg6p/agf9nQGaiWPBMsPF16/PdChm0NjAmShrU3YLH0H+LbJzR12beMcvQuAA/saOIpsNF9bWBC799sjwektxmn7bTs/fT8bq7WX5ExzQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000041, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Jeongjun Park wrote: > > I got the following KCSAN report during syzbot testing: > > ================================================================== > BUG: KCSAN: data-race in generic_fillattr / inode_set_ctime_current > > write to 0xffff888102eb3260 of 4 bytes by task 6565 on cpu 1: > inode_set_ctime_to_ts include/linux/fs.h:1638 [inline] > inode_set_ctime_current+0x169/0x1d0 fs/inode.c:2626 > shmem_mknod+0x117/0x180 mm/shmem.c:3443 > shmem_create+0x34/0x40 mm/shmem.c:3497 > lookup_open fs/namei.c:3578 [inline] > open_last_lookups fs/namei.c:3647 [inline] > path_openat+0xdbc/0x1f00 fs/namei.c:3883 > do_filp_open+0xf7/0x200 fs/namei.c:3913 > do_sys_openat2+0xab/0x120 fs/open.c:1416 > do_sys_open fs/open.c:1431 [inline] > __do_sys_openat fs/open.c:1447 [inline] > __se_sys_openat fs/open.c:1442 [inline] > __x64_sys_openat+0xf3/0x120 fs/open.c:1442 > x64_sys_call+0x1025/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:258 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0x54/0x120 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > read to 0xffff888102eb3260 of 4 bytes by task 3498 on cpu 0: > inode_get_ctime_nsec include/linux/fs.h:1623 [inline] > inode_get_ctime include/linux/fs.h:1629 [inline] > generic_fillattr+0x1dd/0x2f0 fs/stat.c:62 > shmem_getattr+0x17b/0x200 mm/shmem.c:1157 > vfs_getattr_nosec fs/stat.c:166 [inline] > vfs_getattr+0x19b/0x1e0 fs/stat.c:207 > vfs_statx_path fs/stat.c:251 [inline] > vfs_statx+0x134/0x2f0 fs/stat.c:315 > vfs_fstatat+0xec/0x110 fs/stat.c:341 > __do_sys_newfstatat fs/stat.c:505 [inline] > __se_sys_newfstatat+0x58/0x260 fs/stat.c:499 > __x64_sys_newfstatat+0x55/0x70 fs/stat.c:499 > x64_sys_call+0x141f/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:263 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0x54/0x120 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > value changed: 0x2755ae53 -> 0x27ee44d3 > > Since there is no special protection when shmem_getattr() calls > generic_fillattr(), data-race occurs by functions such as shmem_unlink() > or shmem_mknod(). This can cause unexpected results, so commenting it out > is not enough. > > Therefore, when calling generic_fillattr() from shmem_getattr(), it is > appropriate to protect the inode using inode_lock_shared() and > inode_unlock_shared() to prevent data-race. > Cc: stable@vger.kernel.org I think this patch should be applied from next rc version and also stable version. When calling generic_fillattr(), if you don't hold read lock, data-race will occur in inode member variables, which can cause unexpected behavior. This problem is also present in several stable versions, so I think it should be fixed as soon as possible. Regards, Jeongjun Park > Reported-by: syzbot > Fixes: 44a30220bc0a ("shmem: recalculate file inode when fstat") > Signed-off-by: Jeongjun Park > --- > mm/shmem.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 5a77acf6ac6a..9beeb47c3743 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1154,7 +1154,9 @@ static int shmem_getattr(struct mnt_idmap *idmap, > stat->attributes_mask |= (STATX_ATTR_APPEND | > STATX_ATTR_IMMUTABLE | > STATX_ATTR_NODUMP); > + inode_lock_shared(inode); > generic_fillattr(idmap, request_mask, inode, stat); > + inode_unlock_shared(inode); > > if (shmem_is_huge(inode, 0, false, NULL, 0)) > stat->blksize = HPAGE_PMD_SIZE; > --