[PATCH 4.14 58/59] ext4: add reclaim checks to xattr code

Greg Kroah-Hartman
2021-03-29T08:12:58Z

From: Jan Kara <jack@suse.cz>

commit 163f0ec1df33cf468509ff38cbcbb5eb0d7fac60 upstream.

Syzbot is reporting that ext4 can enter fs reclaim from kvmalloc() while
the transaction is started like:

fs_reclaim_acquire+0x117/0x150 mm/page_alloc.c:4340
might_alloc include/linux/sched/mm.h:193 [inline]
slab_pre_alloc_hook mm/slab.h:493 [inline]
slab_alloc_node mm/slub.c:2817 [inline]
__kmalloc_node+0x5f/0x430 mm/slub.c:4015
kmalloc_node include/linux/slab.h:575 [inline]
kvmalloc_node+0x61/0xf0 mm/util.c:587
kvmalloc include/linux/mm.h:781 [inline]
ext4_xattr_inode_cache_find fs/ext4/xattr.c:1465 [inline]
ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1508 [inline]
ext4_xattr_set_entry+0x1ce6/0x3780 fs/ext4/xattr.c:1649
ext4_xattr_ibody_set+0x78/0x2b0 fs/ext4/xattr.c:2224
ext4_xattr_set_handle+0x8f4/0x13e0 fs/ext4/xattr.c:2380
ext4_xattr_set+0x13a/0x340 fs/ext4/xattr.c:2493

This should be impossible since transaction start sets PF_MEMALLOC_NOFS.
Add some assertions to the code to catch if something isn't working as
expected early.

Link: https://lore.kernel.org/linux-ext4/000000000000563a0205bafb7970@google.com/
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210222171626.21884-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/xattr.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1479,6 +1479,9 @@ ext4_xattr_inode_cache_find(struct inode
if (!ce)
return NULL;

+ WARN_ON_ONCE(ext4_handle_valid(journal_current_handle()) &&
+ !(current->flags & PF_MEMALLOC_NOFS));
+
ea_data = ext4_kvmalloc(value_len, GFP_NOFS);
if (!ea_data) {
mb_cache_entry_put(ea_inode_cache, ce);
@@ -2345,6 +2348,7 @@ ext4_xattr_set_handle(handle_t *handle,
error = -ENOSPC;
goto cleanup;
}
+ WARN_ON_ONCE(!(current->flags & PF_MEMALLOC_NOFS));
}

error = ext4_reserve_inode_write(handle, inode, &is.iloc);