| Message ID | 1582660388-28735-1-git-send-email-cai@lca.pw (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | [v2] xfs: fix an undefined behaviour in _da3_path_shift | expand |
On Tue, Feb 25, 2020 at 02:53:08PM -0500, Qian Cai wrote: > xfs_da3_path_shift() could see state->path.blk[-1] because > state->path.active == 1 is a valid state when it tries to add an entry > to a single dir leaf block and then to shift forward to see if > there's a sibling block that would be a better place to put the new > entry. I think this needs a better explanation. Something like: In xfs_da3_path_shift() blk can be assigned to state->path.blk[-1] if state->path.active is 1 (which is a valid state) when it tries to add an entry > to a single dir leaf block and then to shift forward to see if there's a sibling block that would be a better place to put the new entry. This causes a KASAN warning given negative array indices are undefined behavior in C. In practice the warning is entirely harmless given that blk is never dereference in this case, but it is still better to fix up the warning and slightly improve the code.
> On Feb 25, 2020, at 4:40 PM, Christoph Hellwig <hch@infradead.org> wrote: > > In xfs_da3_path_shift() blk can be assigned to state->path.blk[-1] if > state->path.active is 1 (which is a valid state) when it tries to add an > entry > to a single dir leaf block and then to shift forward to see if > there's a sibling block that would be a better place to put the new > entry. This causes a KASAN warning given s/KASAN/UBSAN/ > negative array indices are > undefined behavior in C. In practice the warning is entirely harmless > given that blk is never dereference in this case, but it is still better > to fix up the warning and slightly improve the code. Agree. This is better. Darrick, do you need me to send a v3 for it or you could squash this in?
On Tue, Feb 25, 2020 at 04:55:56PM -0500, Qian Cai wrote: > > > > On Feb 25, 2020, at 4:40 PM, Christoph Hellwig <hch@infradead.org> wrote: > > > > In xfs_da3_path_shift() blk can be assigned to state->path.blk[-1] if > > state->path.active is 1 (which is a valid state) when it tries to add an > > entry > to a single dir leaf block and then to shift forward to see if > > there's a sibling block that would be a better place to put the new > > entry. This causes a KASAN warning given > > s/KASAN/UBSAN/ > > > negative array indices are > > undefined behavior in C. In practice the warning is entirely harmless > > given that blk is never dereference in this case, but it is still better > > to fix up the warning and slightly improve the code. > > Agree. This is better. > > Darrick, do you need me to send a v3 for it or you could squash this in? Please send a v3. The code in v2 looked fine to me. --D
diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c index 875e04f82541..e864c3d47f60 100644 --- a/fs/xfs/libxfs/xfs_da_btree.c +++ b/fs/xfs/libxfs/xfs_da_btree.c @@ -1986,7 +1986,8 @@ 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--) { + for (; level >= 0; level--) { + blk = &path->blk[level]; xfs_da3_node_hdr_from_disk(dp->i_mount, &nodehdr, blk->bp->b_addr);
xfs_da3_path_shift() could see state->path.blk[-1] because state->path.active == 1 is a valid state when it tries to add an entry to a single dir leaf block and then to shift forward to see if there's a sibling block that would be a better place to put the new entry. 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 Suggested-by: Christoph Hellwig <hch@infradead.org> Signed-off-by: Qian Cai <cai@lca.pw> --- v2: update the commit log thanks to Darrick. simplify the code. fs/xfs/libxfs/xfs_da_btree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)