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ext4: fix use-after-free in ext4_ext_shift_extents 

If the starting position of our insert range happens to be in the hole
between the two ext4_extent_idx, because the lblk of the ext4_extent in
the previous ext4_extent_idx is always less than the start, which leads
to the "extent" variable access across the boundary, the following UAF is
triggered:
==================================================================
BUG: KASAN: use-after-free in ext4_ext_shift_extents+0x257/0x790
Read of size 4 at addr ffff88819807a008 by task fallocate/8010
CPU: 3 PID: 8010 Comm: fallocate Tainted: G            E     5.10.0+ #492
Call Trace:
 dump_stack+0x7d/0xa3
 print_address_description.constprop.0+0x1e/0x220
 kasan_report.cold+0x67/0x7f
 ext4_ext_shift_extents+0x257/0x790
 ext4_insert_range+0x5b6/0x700
 ext4_fallocate+0x39e/0x3d0
 vfs_fallocate+0x26f/0x470
 ksys_fallocate+0x3a/0x70
 __x64_sys_fallocate+0x4f/0x60
 do_syscall_64+0x33/0x40
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
==================================================================

For right shifts, we can divide them into the following situations：

1. When the first ee_block of ext4_extent_idx is greater than or equal to
   start, make right shifts directly from the first ee_block.
    1) If it is greater than start, we need to continue searching in the
       previous ext4_extent_idx.
    2) If it is equal to start, we can exit the loop (iterator=NULL).

2. When the first ee_block of ext4_extent_idx is less than start, then
   traverse from the last extent to find the first extent whose ee_block
   is less than start.
    1) If extent is still the last extent after traversal, it means that
       the last ee_block of ext4_extent_idx is less than start, that is,
       start is located in the hole between idx and (idx+1), so we can
       exit the loop directly (break) without right shifts.
    2) Otherwise, make right shifts at the corresponding position of the
       found extent, and then exit the loop (iterator=NULL).

Fixes: 331573febb ("ext4: Add support FALLOC_FL_INSERT_RANGE for fallocate")
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Link: https://lore.kernel.org/r/20220922120434.1294789-1-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Baokun Li 2022-09-22 20:04:34 +08:00 committed by Theodore Ts'o
parent f0c4d9fc9c
commit f6b1a1cf1c
1 changed files with 13 additions and 5 deletions
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18
fs/ext4/extents.c
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@ -5184,6 +5184,7 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
* and it is decreased till we reach start.
*/
again:
ret = 0;
if (SHIFT == SHIFT_LEFT)
iterator = &start;
else
@ -5227,14 +5228,21 @@ again:
ext4_ext_get_actual_len(extent);
} else {
extent = EXT_FIRST_EXTENT(path[depth].p_hdr);
if (le32_to_cpu(extent->ee_block) > 0)
if (le32_to_cpu(extent->ee_block) > start)
*iterator = le32_to_cpu(extent->ee_block) - 1;
else
/* Beginning is reached, end of the loop */
else if (le32_to_cpu(extent->ee_block) == start)
iterator = NULL;
/* Update path extent in case we need to stop */
while (le32_to_cpu(extent->ee_block) < start)
else {
extent = EXT_LAST_EXTENT(path[depth].p_hdr);
while (le32_to_cpu(extent->ee_block) >= start)
extent--;
if (extent == EXT_LAST_EXTENT(path[depth].p_hdr))
break;
extent++;
iterator = NULL;
}
path[depth].p_ext = extent;
}
ret = ext4_ext_shift_path_extents(path, shift, inode,