Patch "ext4: verify extent header depth" has been added to the 4.7-stable tree

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

ext4: verify extent header depth

to the 4.7-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-verify-extent-header-depth.patch
and it can be found in the queue-4.7 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: Fri, 15 Jul 2016 00:22:07 -0400
Subject: ext4: verify extent header depth

From: Vegard Nossum <[email protected]>

commit 7bc9491645118c9461bd21099c31755ff6783593 upstream.

Although the extent tree depth of 5 should enough be for the worst case of 2*32 extents of length 1, the extent tree code does not currently to merge nodes which are less than half-full with a sibling node, or to shrink the tree depth if possible. So it's possible, at least in theory, for the tree depth to be greater than 5. However, even in the worst case, a tree depth of 32 is highly unlikely, and if the file system is maliciously corrupted, an insanely large eh_depth can cause memory allocation failures that will trigger kernel warnings (here, eh_depth = 65280):

    JBD2: ext4.exe wants too many credits credits:195849 rsv_credits:0 max:256
    ------------[ cut here ]------------
    WARNING: CPU: 0 PID: 50 at fs/jbd2/transaction.c:293 start_this_handle+0x569/0x580
    CPU: 0 PID: 50 Comm: ext4.exe Not tainted 4.7.0-rc5+ #508
    Stack:
     604a8947 625badd8 0002fd09 00000000
     60078643 00000000 62623910 601bf9bc
     62623970 6002fc84 626239b0 900000125
    Call Trace:
     [<6001c2dc>] show_stack+0xdc/0x1a0
     [<601bf9bc>] dump_stack+0x2a/0x2e
     [<6002fc84>] __warn+0x114/0x140
     [<6002fdff>] warn_slowpath_null+0x1f/0x30
     [<60165829>] start_this_handle+0x569/0x580
     [<60165d4e>] jbd2__journal_start+0x11e/0x220
     [<60146690>] __ext4_journal_start_sb+0x60/0xa0
     [<60120a81>] ext4_truncate+0x131/0x3a0
     [<60123677>] ext4_setattr+0x757/0x840
     [<600d5d0f>] notify_change+0x16f/0x2a0
     [<600b2b16>] do_truncate+0x76/0xc0
     [<600c3e56>] path_openat+0x806/0x1300
     [<600c55c9>] do_filp_open+0x89/0xf0
     [<600b4074>] do_sys_open+0x134/0x1e0
     [<600b4140>] SyS_open+0x20/0x30
     [<6001ea68>] handle_syscall+0x88/0x90
     [<600295fd>] userspace+0x3fd/0x500
     [<6001ac55>] fork_handler+0x85/0x90

    ---[ end trace 08b0b88b6387a244 ]---

[ Commit message modified and the extent tree depath check changed from 5 to 32 -- tytso ]

---
 fs/ext4/extents.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -474,6 +474,10 @@ static int __ext4_ext_check(const char *
 		error_msg = "invalid extent entries";
 		goto corrupted;
 	}
+	if (unlikely(depth > 32)) {
+		error_msg = "too large eh_depth";
+		goto corrupted;
+	}
 	/* Verify checksum on non-root extent tree nodes */
 	if (ext_depth(inode) != depth &&
 	    !ext4_extent_block_csum_verify(inode, eh)) {

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

queue-4.7/ext4-verify-extent-header-depth.patch