From: yangerkun <yangerkun@xxxxxxxxxx> commit d7dce9e08595e80bf8039a81794809c66fe26431 upstream. ext4_ext_search_right() will read more extent blocks and call put_bh after we get the information we need. However, ret_ex will break this and may cause use-after-free once pagecache has been freed. Fix it by copying the extent structure if needed. Signed-off-by: yangerkun <yangerkun@xxxxxxxxxx> Link: https://lore.kernel.org/r/20201028055617.2569255-1-yangerkun@xxxxxxxxxx Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> Cc: stable@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/ext4/extents.c | 30 +++++++++++++++--------------- 1 file changed, 15 insertions(+), 15 deletions(-) --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -1472,16 +1472,16 @@ static int ext4_ext_search_left(struct i } /* - * search the closest allocated block to the right for *logical - * and returns it at @logical + it's physical address at @phys - * if *logical is the largest allocated block, the function - * returns 0 at @phys - * return value contains 0 (success) or error code + * Search the closest allocated block to the right for *logical + * and returns it at @logical + it's physical address at @phys. + * If not exists, return 0 and @phys is set to 0. We will return + * 1 which means we found an allocated block and ret_ex is valid. + * Or return a (< 0) error code. */ static int ext4_ext_search_right(struct inode *inode, struct ext4_ext_path *path, ext4_lblk_t *logical, ext4_fsblk_t *phys, - struct ext4_extent **ret_ex) + struct ext4_extent *ret_ex) { struct buffer_head *bh = NULL; struct ext4_extent_header *eh; @@ -1575,10 +1575,11 @@ got_index: found_extent: *logical = le32_to_cpu(ex->ee_block); *phys = ext4_ext_pblock(ex); - *ret_ex = ex; + if (ret_ex) + *ret_ex = *ex; if (bh) put_bh(bh); - return 0; + return 1; } /* @@ -2869,8 +2870,8 @@ again: */ lblk = ex_end + 1; err = ext4_ext_search_right(inode, path, &lblk, &pblk, - &ex); - if (err) + NULL); + if (err < 0) goto out; if (pblk) { partial.pclu = EXT4_B2C(sbi, pblk); @@ -4038,7 +4039,7 @@ int ext4_ext_map_blocks(handle_t *handle struct ext4_map_blocks *map, int flags) { struct ext4_ext_path *path = NULL; - struct ext4_extent newex, *ex, *ex2; + struct ext4_extent newex, *ex, ex2; struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); ext4_fsblk_t newblock = 0, pblk; int err = 0, depth, ret; @@ -4174,15 +4175,14 @@ int ext4_ext_map_blocks(handle_t *handle if (err) goto out; ar.lright = map->m_lblk; - ex2 = NULL; err = ext4_ext_search_right(inode, path, &ar.lright, &ar.pright, &ex2); - if (err) + if (err < 0) goto out; /* Check if the extent after searching to the right implies a * cluster we can use. */ - if ((sbi->s_cluster_ratio > 1) && ex2 && - get_implied_cluster_alloc(inode->i_sb, map, ex2, path)) { + if ((sbi->s_cluster_ratio > 1) && err && + get_implied_cluster_alloc(inode->i_sb, map, &ex2, path)) { ar.len = allocated = map->m_len; newblock = map->m_pblk; goto got_allocated_blocks;
