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ext4: avoid use-after-free in ext4_ext_show_leaf()

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In ext4_find_extent(), path may be freed by error or be reallocated, so
using a previously saved *ppath may have been freed and thus may trigger
use-after-free, as follows:

ext4_split_extent
  path = *ppath;
  ext4_split_extent_at(ppath)
  path = ext4_find_extent(ppath)
  ext4_split_extent_at(ppath)
    // ext4_find_extent fails to free path
    // but zeroout succeeds
  ext4_ext_show_leaf(inode, path)
    eh = path[depth].p_hdr
    // path use-after-free !!!

Similar to ext4_split_extent_at(), we use *ppath directly as an input to
ext4_ext_show_leaf(). Fix a spelling error by the way.

Same problem in ext4_ext_handle_unwritten_extents(). Since 'path' is only
used in ext4_ext_show_leaf(), remove 'path' and use *ppath directly.

This issue is triggered only when EXT_DEBUG is defined and therefore does
not affect functionality.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Tested-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://patch.msgid.link/20240822023545.1994557-5-libaokun@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Baokun Li 2024-08-22 10:35:24 +08:00 committed by Theodore Ts'o
parent c26ab35702
commit 4e2524ba2c
1 changed files with 4 additions and 5 deletions
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9
fs/ext4/extents.c
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@ -3327,7 +3327,7 @@ out:
} }
/* /*
* ext4_split_extents() splits an extent and mark extent which is covered * ext4_split_extent() splits an extent and mark extent which is covered
* by @map as split_flags indicates * by @map as split_flags indicates
* *
* It may result in splitting the extent into multiple extents (up to three) * It may result in splitting the extent into multiple extents (up to three)
@ -3403,7 +3403,7 @@ static int ext4_split_extent(handle_t *handle,
goto out; goto out;
} }
ext4_ext_show_leaf(inode, path); ext4_ext_show_leaf(inode, *ppath);
out: out:
return err ? err : allocated; return err ? err : allocated;
} }
@ -3868,14 +3868,13 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
struct ext4_ext_path **ppath, int flags, struct ext4_ext_path **ppath, int flags,
unsigned int allocated, ext4_fsblk_t newblock) unsigned int allocated, ext4_fsblk_t newblock)
{ {
struct ext4_ext_path __maybe_unused *path = *ppath;
int ret = 0; int ret = 0;
int err = 0; int err = 0;
ext_debug(inode, "logical block %llu, max_blocks %u, flags 0x%x, allocated %u\n", ext_debug(inode, "logical block %llu, max_blocks %u, flags 0x%x, allocated %u\n",
(unsigned long long)map->m_lblk, map->m_len, flags, (unsigned long long)map->m_lblk, map->m_len, flags,
allocated); allocated);
ext4_ext_show_leaf(inode, path); ext4_ext_show_leaf(inode, *ppath);
/* /*
* When writing into unwritten space, we should not fail to * When writing into unwritten space, we should not fail to
@ -3972,7 +3971,7 @@ out1:
if (allocated > map->m_len) if (allocated > map->m_len)
allocated = map->m_len; allocated = map->m_len;
map->m_len = allocated; map->m_len = allocated;
ext4_ext_show_leaf(inode, path); ext4_ext_show_leaf(inode, *ppath);
out2: out2:
return err ? err : allocated; return err ? err : allocated;
} }