Patch "ext4: avoid use-after-free in ext4_ext_show_leaf()" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ext4-avoid-use-after-free-in-ext4_ext_show_leaf.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 1c03f4dc7d57bdb7d2d13b4872cda0bb18b45ec2
Author: Baokun Li <libaokun1@xxxxxxxxxx>
Date:   Thu Aug 22 10:35:24 2024 +0800

    ext4: avoid use-after-free in ext4_ext_show_leaf()
    
    [ Upstream commit 4e2524ba2ca5f54bdbb9e5153bea00421ef653f5 ]
    
    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@xxxxxxxxxx>
    Reviewed-by: Jan Kara <jack@xxxxxxx>
    Reviewed-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
    Tested-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
    Link: https://patch.msgid.link/20240822023545.1994557-5-libaokun@xxxxxxxxxxxxxxx
    Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index a3869e9c71b91..1e52f90ddee43 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3288,7 +3288,7 @@ static int ext4_split_extent_at(handle_t *handle,
 }
 
 /*
- * 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
  *
  * It may result in splitting the extent into multiple extents (up to three)
@@ -3365,7 +3365,7 @@ static int ext4_split_extent(handle_t *handle,
 			goto out;
 	}
 
-	ext4_ext_show_leaf(inode, path);
+	ext4_ext_show_leaf(inode, *ppath);
 out:
 	return err ? err : allocated;
 }
@@ -3831,14 +3831,13 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
 			struct ext4_ext_path **ppath, int flags,
 			unsigned int allocated, ext4_fsblk_t newblock)
 {
-	struct ext4_ext_path __maybe_unused *path = *ppath;
 	int ret = 0;
 	int err = 0;
 
 	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,
 		  allocated);
-	ext4_ext_show_leaf(inode, path);
+	ext4_ext_show_leaf(inode, *ppath);
 
 	/*
 	 * When writing into unwritten space, we should not fail to
@@ -3935,7 +3934,7 @@ ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
 	if (allocated > map->m_len)
 		allocated = map->m_len;
 	map->m_len = allocated;
-	ext4_ext_show_leaf(inode, path);
+	ext4_ext_show_leaf(inode, *ppath);
 out2:
 	return err ? err : allocated;
 }