[PATCH] xfs: fix an undefined behaviour in _da3_path_shift

Qian Cai
2020-02-25T14:38:16Z

state->path.active could be 1 in xfs_da3_node_lookup_int() and then in
xfs_da3_path_shift() could see state->path.blk[-1].

UBSAN: Undefined behaviour in fs/xfs/libxfs/xfs_da_btree.c:1989:14
index -1 is out of range for type 'xfs_da_state_blk_t [5]'
Call trace:
dump_backtrace+0x0/0x2c8
show_stack+0x20/0x2c
dump_stack+0xe8/0x150
__ubsan_handle_out_of_bounds+0xe4/0xfc
xfs_da3_path_shift+0x860/0x86c [xfs]
xfs_da3_node_lookup_int+0x7c8/0x934 [xfs]
xfs_dir2_node_addname+0x2c8/0xcd0 [xfs]
xfs_dir_createname+0x348/0x38c [xfs]
xfs_create+0x6b0/0x8b4 [xfs]
xfs_generic_create+0x12c/0x1f8 [xfs]
xfs_vn_mknod+0x3c/0x4c [xfs]
xfs_vn_create+0x34/0x44 [xfs]
do_last+0xd4c/0x10c8
path_openat+0xbc/0x2f4
do_filp_open+0x74/0xf4
do_sys_openat2+0x98/0x180
__arm64_sys_openat+0xf8/0x170
do_el0_svc+0x170/0x240
el0_sync_handler+0x150/0x250
el0_sync+0x164/0x180

Signed-off-by: Qian Cai <cai@lca.pw>
---
fs/xfs/libxfs/xfs_da_btree.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
index 875e04f82541..0906b7748a3f 100644
--- a/fs/xfs/libxfs/xfs_da_btree.c
+++ b/fs/xfs/libxfs/xfs_da_btree.c
@@ -1986,7 +1986,11 @@ static inline int xfs_dabuf_nfsb(struct xfs_mount *mp, int whichfork)
ASSERT(path != NULL);
ASSERT((path->active > 0) && (path->active < XFS_DA_NODE_MAXDEPTH));
level = (path->active-1) - 1; /* skip bottom layer in path */
- for (blk = &path->blk[level]; level >= 0; blk--, level--) {
+
+ if (level >= 0)
+ blk = &path->blk[level];
+
+ for (; level >= 0; blk--, level--) {
xfs_da3_node_hdr_from_disk(dp->i_mount, &nodehdr,
blk->bp->b_addr);

--
1.8.3.1