patch "staging: erofs: fix illegal address access under memory pressure" added to staging-next

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

staging: erofs: fix illegal address access under memory pressure

to my staging git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

From 1e5ceeab6929585512c63d05911d6657064abf7b Mon Sep 17 00:00:00 2001
From: Gao Xiang <[email protected]>
Date: Wed, 27 Feb 2019 13:33:31 +0800
Subject: staging: erofs: fix illegal address access under memory pressure

Considering a read request with two decompressed file pages, If a decompression work cannot be started on the previous page due to memory pressure but in-memory LTP map lookup is done, builder->work should be still NULL.

Moreover, if the current page also belongs to the same map, it won't try to start the decompression work again and then run into trouble.

This patch aims to solve the above issue only with little changes as much as possible in order to make the fix backport easier.

kernel message is:
<4>[1051408.015930s]SLUB: Unable to allocate memory on node -1, gfp=0x2408040(GFP_NOFS|__GFP_ZERO) <4>[1051408.015930s] cache: erofs_compress, object size: 144, buffer size: 144, default order: 0, min order: 0 <4>[1051408.015930s] node 0: slabs: 98, objs: 2744, free: 0
* Cannot allocate the decompression work

<3>[1051408.015960s]erofs: z_erofs_vle_normalaccess_readpages, readahead error at page 1008 of nid 5391488
* Note that the previous page was failed to read

<0>[1051408.015960s]Internal error: Accessing user space memory outside uaccess.h routines: 96000005 [#1] PREEMPT SMP
...
<4>[1051408.015991s]Hardware name: kirin710 (DT)
...
<4>[1051408.016021s]PC is at z_erofs_vle_work_add_page+0xa0/0x17c
<4>[1051408.016021s]LR is at z_erofs_do_read_page+0x12c/0xcf0
...
<4>[1051408.018096s][<ffffff80c6fb0fd4>] z_erofs_vle_work_add_page+0xa0/0x17c <4>[1051408.018096s][<ffffff80c6fb3814>] z_erofs_vle_normalaccess_readpages+0x1a0/0x37c <4>[1051408.018096s][<ffffff80c6d670b8>] read_pages+0x70/0x190 <4>[1051408.018127s][<ffffff80c6d6736c>] __do_page_cache_readahead+0x194/0x1a8 <4>[1051408.018127s][<ffffff80c6d59318>] filemap_fault+0x398/0x684 <4>[1051408.018127s][<ffffff80c6d8a9e0>] __do_fault+0x8c/0x138 <4>[1051408.018127s][<ffffff80c6d8f90c>] handle_pte_fault+0x730/0xb7c <4>[1051408.018127s][<ffffff80c6d8fe04>] __handle_mm_fault+0xac/0xf4 <4>[1051408.018157s][<ffffff80c6d8fec8>] handle_mm_fault+0x7c/0x118 <4>[1051408.018157s][<ffffff80c8c52998>] do_page_fault+0x354/0x474 <4>[1051408.018157s][<ffffff80c8c52af8>] do_translation_fault+0x40/0x48 <4>[1051408.018157s][<ffffff80c6c002f4>] do_mem_abort+0x80/0x100
<4>[1051408.018310s]---[ end trace 9f4009a3283bd78b ]---

---
 drivers/staging/erofs/unzip_vle.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

index 416dde4e8ea1..74c13b0a3d33 100644
@@ -698,8 +698,12 @@ static int z_erofs_do_read_page(struct z_erofs_vle_frontend *fe,
 
 	/* lucky, within the range of the current map_blocks */
 	if (offset + cur >= map->m_la &&
-		offset + cur < map->m_la + map->m_llen)
+		offset + cur < map->m_la + map->m_llen) {
+		/* didn't get a valid unzip work previously (very rare) */
+		if (!builder->work)
+			goto restart_now;
 		goto hitted;
+	}
 
 	/* go ahead the next map_blocks */
 	debugln("%s: [out-of-range] pos %llu", __func__, offset + cur);

@@ -713,6 +717,7 @@ static int z_erofs_do_read_page(struct z_erofs_vle_frontend *fe,
 	if (unlikely(err))
 		goto err_out;
 
+restart_now:
 	if (unlikely(!(map->m_flags & EROFS_MAP_MAPPED)))
 		goto hitted;
 

2.21.0