From: Darrick J. Wong <darrick.wong@xxxxxxxxxx> For VFS listxattr calls, xfs_xattr_put_listent calls __xfs_xattr_put_listent twice if it sees an attribute "trusted.SGI_ACL_FILE": once for that name, and again for "system.posix_acl_access". Unfortunately, if we happen to run out of buffer space while emitting the first name, we set count to -1 (so that we can feed ERANGE to the caller). The second invocation doesn't check that the context parameters make sense and overwrites the byte before the buffer, triggering a KASAN report: ================================================================== BUG: KASAN: slab-out-of-bounds in strncpy+0xb3/0xd0 Write of size 1 at addr ffff88807fbd317f by task syz/1113 CPU: 3 PID: 1113 Comm: syz Not tainted 5.0.0-rc6-xfsx #rc6 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1ubuntu1 04/01/2014 Call Trace: dump_stack+0xcc/0x180 print_address_description+0x6c/0x23c kasan_report.cold.3+0x1c/0x35 strncpy+0xb3/0xd0 __xfs_xattr_put_listent+0x1a9/0x2c0 [xfs] xfs_attr_list_int_ilocked+0x11af/0x1800 [xfs] xfs_attr_list_int+0x20c/0x2e0 [xfs] xfs_vn_listxattr+0x225/0x320 [xfs] listxattr+0x11f/0x1b0 path_listxattr+0xbd/0x130 do_syscall_64+0x139/0x560 While we're at it we add an assert to the other put_listent to avoid this sort of thing ever happening to the attrlist_by_handle code. Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> --- fs/xfs/xfs_attr_list.c | 1 + fs/xfs/xfs_xattr.c | 3 +++ 2 files changed, 4 insertions(+) diff --git a/fs/xfs/xfs_attr_list.c b/fs/xfs/xfs_attr_list.c index a58034049995..3d213a7394c5 100644 --- a/fs/xfs/xfs_attr_list.c +++ b/fs/xfs/xfs_attr_list.c @@ -555,6 +555,7 @@ xfs_attr_put_listent( attrlist_ent_t *aep; int arraytop; + ASSERT(!context->seen_enough); ASSERT(!(context->flags & ATTR_KERNOVAL)); ASSERT(context->count >= 0); ASSERT(context->count < (ATTR_MAX_VALUELEN/8)); diff --git a/fs/xfs/xfs_xattr.c b/fs/xfs/xfs_xattr.c index 63ee1d5bf1d7..9a63016009a1 100644 --- a/fs/xfs/xfs_xattr.c +++ b/fs/xfs/xfs_xattr.c @@ -129,6 +129,9 @@ __xfs_xattr_put_listent( char *offset; int arraytop; + if (context->count < 0 || context->seen_enough) + return; + if (!context->alist) goto compute_size;
