Patch "ext4: fix reference counting bug on block allocation error" has been added to the 4.6-stable tree

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

ext4: fix reference counting bug on block allocation error

to the 4.6-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-fix-reference-counting-bug-on-block-allocation-error.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Vegard Nossum <[email protected]>
Date: Thu, 14 Jul 2016 23:02:47 -0400
Subject: ext4: fix reference counting bug on block allocation error

From: Vegard Nossum <[email protected]>

commit 554a5ccc4e4a20c5f3ec859de0842db4b4b9c77e upstream.

If we hit this error when mounted with errors=continue or errors=remount-ro:

EXT4-fs error (device loop0): ext4_mb_mark_diskspace_used:2940: comm ext4.exe: Allocating blocks 5090-6081 which overlap fs metadata

then ext4_mb_new_blocks() will call ext4_mb_release_context() and try to continue. However, ext4_mb_release_context() is the wrong thing to call here since we are still actually using the allocation context.

Instead, just error out. We could retry the allocation, but there is a possibility of getting stuck in an infinite loop instead, so this seems safer.

[ Fixed up so we don't return EAGAIN to userspace. --tytso ]

---
 fs/ext4/mballoc.c |   17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

@@ -2939,7 +2939,7 @@ ext4_mb_mark_diskspace_used(struct ext4_
 		ext4_error(sb, "Allocating blocks %llu-%llu which overlap "
 			   "fs metadata", block, block+len);
 		/* File system mounted not to panic on error
-		 * Fix the bitmap and repeat the block allocation
+		 * Fix the bitmap and return EFSCORRUPTED
 		 * We leak some of the blocks here.
 		 */
 		ext4_lock_group(sb, ac->ac_b_ex.fe_group);

@@ -2948,7 +2948,7 @@ ext4_mb_mark_diskspace_used(struct ext4_
 		ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
 		err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
 		if (!err)
-			err = -EAGAIN;
+			err = -EFSCORRUPTED;
 		goto out_err;
 	}
 

@@ -4513,18 +4513,7 @@ repeat:
 	}
 	if (likely(ac->ac_status == AC_STATUS_FOUND)) {
 		*errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_clstrs);
-		if (*errp == -EAGAIN) {
-			/*
-			 * drop the reference that we took
-			 * in ext4_mb_use_best_found
-			 */
-			ext4_mb_release_context(ac);
-			ac->ac_b_ex.fe_group = 0;
-			ac->ac_b_ex.fe_start = 0;
-			ac->ac_b_ex.fe_len = 0;
-			ac->ac_status = AC_STATUS_CONTINUE;
-			goto repeat;
-		} else if (*errp) {
+		if (*errp) {
 			ext4_discard_allocated_blocks(ac);
 			goto errout;
 		} else {

Patches currently in stable-queue which might be from [email protected] are

queue-4.6/ext4-short-cut-orphan-cleanup-on-error.patch queue-4.6/block-fix-use-after-free-in-seq-file.patch queue-4.6/ext4-check-for-extents-that-wrap-around.patch queue-4.6/net-irda-fix-null-pointer-dereference-on-memory-allocation-failure.patch queue-4.6/ext4-validate-s_reserved_gdt_blocks-on-mount.patch queue-4.6/ext4-don-t-call-ext4_should_journal_data-on-the-journal-inode.patch queue-4.6/ext4-fix-reference-counting-bug-on-block-allocation-error.patch