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Sun, 16 Aug 2026 11:56:13 -0700 (PDT) Received: from TheRealOne ([2409:40e1:45f:d5b0:d158:6a04:1e7e:a9b8]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-320e9df03ecsm29934885eec.18.2026.08.16.11.56.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 16 Aug 2026 11:56:13 -0700 (PDT) From: Chandradhar Kumar To: dhowells@redhat.com Cc: netfs@lists.linux.dev, linux-kernel@vger.kernel.org, Chandradhar Kumar , syzbot+62b392c7348147ad767d@syzkaller.appspotmail.com Subject: [PATCH] cachefiles: Fix OOB access in coherency trace Date: Mon, 17 Aug 2026 00:25:48 +0530 Message-ID: <20260816185548.292045-1-chandradhar.2003@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The coherency trace read the first 8 bytes of the auxiliary data with be64_to_cpup(). However the auxiliary data stored in a cachefiles xattr is variable length. 9P uses the 4-byte QID version as auxiliary data. Thus buf->data contains only those 4 bytes, but the coherency trace unconditionally reads 8 bytes from it, causing KASAN slab-out-of-bounds report. Copy up to the first 8 bytes of the auxiliary data into an 8-byte buffer before reading it as a big-endian value. Fixes: 229105e5cfd9 ("cachefiles: Add auxiliary data trace") Reported-by: syzbot+62b392c7348147ad767d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D62b392c7348147ad767d Signed-off-by: Chandradhar Kumar --- fs/cachefiles/xattr.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/fs/cachefiles/xattr.c b/fs/cachefiles/xattr.c index f8ae78b3f7b6..e4cd635e8abe 100644 --- a/fs/cachefiles/xattr.c +++ b/fs/cachefiles/xattr.c @@ -25,6 +25,14 @@ struct cachefiles_xattr { __u8 data[]; /* netfs coherency data */ } __packed; =20 +static u64 cachefiles_get_aux_u64(const void *data, unsigned int len) +{ + __be64 aux =3D 0; + + memcpy(&aux, data, min_t(unsigned int, len, sizeof(aux))); + return be64_to_cpup(&aux); +} + static const char cachefiles_xattr_cache[] =3D XATTR_USER_PREFIX "CacheFiles.cache"; =20 @@ -77,7 +85,7 @@ int cachefiles_set_object_xattr(struct cachefiles_object = *object) trace_cachefiles_vfs_error(object, file_inode(file), ret, cachefiles_trace_setxattr_error); trace_cachefiles_coherency(object, file_inode(file)->i_ino, - be64_to_cpup((__be64 *)buf->data), + cachefiles_get_aux_u64(buf->data, len), buf->content, cachefiles_coherency_set_fail); if (ret !=3D -ENOMEM) @@ -86,7 +94,7 @@ int cachefiles_set_object_xattr(struct cachefiles_object = *object) "Failed to set xattr with error %d", ret); } else { trace_cachefiles_coherency(object, file_inode(file)->i_ino, - be64_to_cpup((__be64 *)buf->data), + cachefiles_get_aux_u64(buf->data, len), buf->content, cachefiles_coherency_set_ok); } @@ -148,7 +156,7 @@ int cachefiles_check_auxdata(struct cachefiles_object *= object, struct file *file =20 out: trace_cachefiles_coherency(object, file_inode(file)->i_ino, - be64_to_cpup((__be64 *)buf->data), + cachefiles_get_aux_u64(buf->data, len), buf->content, why); kfree(buf); return ret; --=20 2.55.0