btrfs: fix invalid leaf access due to inline extent during lseek

During lseek, for SEEK_DATA and SEEK_HOLE modes, we access the disk_bytenr
of an extent without checking its type. However inline extents have their
data starting the offset of the disk_bytenr field, so accessing that field
when we have an inline extent can result in either of the following:

1) Interpret the inline extent's data as a disk_bytenr value;

2) In case the inline data is less than 8 bytes, we access part of some
   other item in the leaf, or unused space in the leaf;

3) In case the inline data is less than 8 bytes and the extent item is
   the first item in the leaf, we can access beyond the leaf's limit.

So fix this by not accessing the disk_bytenr field if we have an inline
extent.

Fixes: b6e8335 ("btrfs: make hole and data seeking a lot more efficient")
Reported-by: Matthias Schoepfer <[email protected]>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216908
Link: https://lore.kernel.org/linux-btrfs/[email protected]/
CC: [email protected] # 6.1
Signed-off-by: Filipe Manana <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: fdmanana

fs/btrfs/file.c

@@ -3541,6 +3541,7 @@ static loff_t find_desired_extent(struct file *file, loff_t offset, int whence)
 		struct extent_buffer *leaf = path->nodes[0];
 		struct btrfs_file_extent_item *extent;
 		u64 extent_end;
+		u8 type;
 
 		if (path->slots[0] >= btrfs_header_nritems(leaf)) {
 			ret = btrfs_next_leaf(root, path);
@@ -3596,10 +3597,16 @@ static loff_t find_desired_extent(struct file *file, loff_t offset, int whence)
 
 		extent = btrfs_item_ptr(leaf, path->slots[0],
 					struct btrfs_file_extent_item);
+		type = btrfs_file_extent_type(leaf, extent);
 
-		if (btrfs_file_extent_disk_bytenr(leaf, extent) == 0 ||
-		    btrfs_file_extent_type(leaf, extent) ==
-		    BTRFS_FILE_EXTENT_PREALLOC) {
+		/*
+		 * Can't access the extent's disk_bytenr field if this is an
+		 * inline extent, since at that offset, it's where the extent
+		 * data starts.
+		 */
+		if (type == BTRFS_FILE_EXTENT_PREALLOC ||
+		    (type == BTRFS_FILE_EXTENT_REG &&
+		     btrfs_file_extent_disk_bytenr(leaf, extent) == 0)) {
 			/*
 			 * Explicit hole or prealloc extent, search for delalloc.
 			 * A prealloc extent is treated like a hole.