staging: zram: fix invalid memory references during disk write

Fixes a bug introduced by commit c8f2f0db1 ("zram: Fix handling
of incompressible pages") which caused invalid memory references
during disk write. Invalid references could occur in two cases:
 - Incoming data expands on compression: In this case, reference was
made to kunmap()'ed bio page.
 - Partial (non PAGE_SIZE) write with incompressible data: In this
case, reference was made to a kfree()'ed buffer.

Fixes bug 50081:
https://bugzilla.kernel.org/show_bug.cgi?id=50081

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Cc: stable <stable@vger.kernel.org>
Reported-by: Mihail Kasadjikov <hamer.mk@gmail.com>
Reported-by: Tomas M <tomas@slax.org>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 24 insertions, 15 deletions

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index fb4a7c94aed..f2a73bd739f 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -265,7 +265,7 @@ out_cleanup:
 static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
                            int offset)
 {
-        int ret;
+        int ret = 0;
         size_t clen;
         unsigned long handle;
         struct page *page;
@@ -286,10 +286,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
                         goto out;
                 }
                 ret = zram_decompress_page(zram, uncmem, index);
-                if (ret) {
-                        kfree(uncmem);
+                if (ret)
                         goto out;
-                }
         }
 
         /*
@@ -302,16 +300,18 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 
         user_mem = kmap_atomic(page);
 
-        if (is_partial_io(bvec))
+        if (is_partial_io(bvec)) {
                 memcpy(uncmem + offset, user_mem + bvec->bv_offset,
                        bvec->bv_len);
-        else
+                kunmap_atomic(user_mem);
+                user_mem = NULL;
+        } else {
                 uncmem = user_mem;
+        }
 
         if (page_zero_filled(uncmem)) {
-                kunmap_atomic(user_mem);
-                if (is_partial_io(bvec))
-                        kfree(uncmem);
+                if (!is_partial_io(bvec))
+                        kunmap_atomic(user_mem);
                 zram_stat_inc(&zram->stats.pages_zero);
                 zram_set_flag(zram, index, ZRAM_ZERO);
                 ret = 0;
@@ -321,9 +321,11 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
         ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen,
                                zram->compress_workmem);
 
-        kunmap_atomic(user_mem);
-        if (is_partial_io(bvec))
-                        kfree(uncmem);
+        if (!is_partial_io(bvec)) {
+                kunmap_atomic(user_mem);
+                user_mem = NULL;
+                uncmem = NULL;
+        }
 
         if (unlikely(ret != LZO_E_OK)) {
                 pr_err("Compression failed! err=%d\n", ret);
@@ -332,8 +334,10 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 
         if (unlikely(clen > max_zpage_size)) {
                 zram_stat_inc(&zram->stats.bad_compress);
-                src = uncmem;
                 clen = PAGE_SIZE;
+                src = NULL;
+                if (is_partial_io(bvec))
+                        src = uncmem;
         }
 
         handle = zs_malloc(zram->mem_pool, clen);
@@ -345,7 +349,11 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
         }
         cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
 
+        if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
+                src = kmap_atomic(page);
         memcpy(cmem, src, clen);
+        if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
+                kunmap_atomic(src);
 
         zs_unmap_object(zram->mem_pool, handle);
 
@@ -358,9 +366,10 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
         if (clen <= PAGE_SIZE / 2)
                 zram_stat_inc(&zram->stats.good_compress);
 
-        return 0;
-
 out:
+        if (is_partial_io(bvec))
+                kfree(uncmem);
+
         if (ret)
                 zram_stat64_inc(zram, &zram->stats.failed_writes);
         return ret;