staging: zram: fix invalid memory references during disk write

Fixes a bug introduced by commit ab4d0a01d ("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>

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index fb4a7c94aed36f087cb41cc771f947b1d6776678..f2a73bd739fb94b750e66e1ee2c931e3c971a52a 100644 (file)
--- 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;