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Date: Mon, 29 Oct 2012 10:14:20 -0700
From: Nitin Gupta <ngupta@...are.org>
To: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Fengguang Wu <fengguang.wu@...el.com>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] zram: factor-out zram_decompress_page() function
On 10/27/2012 09:00 AM, Sergey Senozhatsky wrote:
> zram: factor-out zram_decompress_page() function
>
> zram_bvec_read() shared decompress functionality with zram_read_before_write() function.
> Factor-out and make commonly used zram_decompress_page() function, which also simplified
> error handling in zram_bvec_read().
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
>
> ---
>
> drivers/staging/zram/zram_drv.c | 115 +++++++++++++++++-----------------------
> 1 file changed, 50 insertions(+), 65 deletions(-)
>
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 6edefde..7585467 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -183,62 +183,25 @@ static inline int is_partial_io(struct bio_vec *bvec)
> return bvec->bv_len != PAGE_SIZE;
> }
>
> -static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> - u32 index, int offset, struct bio *bio)
> +static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
> {
> - int ret;
> - size_t clen;
> - struct page *page;
> - unsigned char *user_mem, *cmem, *uncmem = NULL;
> -
> - page = bvec->bv_page;
> -
> - if (zram_test_flag(zram, index, ZRAM_ZERO)) {
> - handle_zero_page(bvec);
> - return 0;
> - }
> + int ret = LZO_E_OK;
> + size_t clen = PAGE_SIZE;
> + unsigned char *cmem;
> + unsigned long handle = zram->table[index].handle;
>
> - /* Requested page is not present in compressed area */
> - if (unlikely(!zram->table[index].handle)) {
> - pr_debug("Read before write: sector=%lu, size=%u",
> - (ulong)(bio->bi_sector), bio->bi_size);
> - handle_zero_page(bvec);
> + if (!handle || zram_test_flag(zram, index, ZRAM_ZERO)) {
> + memset(mem, 0, PAGE_SIZE);
> return 0;
> }
>
> - if (is_partial_io(bvec)) {
> - /* Use a temporary buffer to decompress the page */
> - uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> - if (!uncmem) {
> - pr_info("Error allocating temp memory!\n");
> - return -ENOMEM;
> - }
> - }
> -
> - user_mem = kmap_atomic(page);
> - if (!is_partial_io(bvec))
> - uncmem = user_mem;
> - clen = PAGE_SIZE;
> -
> - cmem = zs_map_object(zram->mem_pool, zram->table[index].handle,
> - ZS_MM_RO);
> -
> - if (zram->table[index].size == PAGE_SIZE) {
> - memcpy(uncmem, cmem, PAGE_SIZE);
> - ret = LZO_E_OK;
> - } else {
> + cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
> + if (zram->table[index].size == PAGE_SIZE)
> + memcpy(mem, cmem, PAGE_SIZE);
> + else
> ret = lzo1x_decompress_safe(cmem, zram->table[index].size,
> - uncmem, &clen);
> - }
> -
> - if (is_partial_io(bvec)) {
> - memcpy(user_mem + bvec->bv_offset, uncmem + offset,
> - bvec->bv_len);
> - kfree(uncmem);
> - }
> -
> - zs_unmap_object(zram->mem_pool, zram->table[index].handle);
> - kunmap_atomic(user_mem);
> + mem, &clen);
> + zs_unmap_object(zram->mem_pool, handle);
>
> /* Should NEVER happen. Return bio error if it does. */
> if (unlikely(ret != LZO_E_OK)) {
> @@ -247,36 +210,58 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> return ret;
> }
>
> - flush_dcache_page(page);
> -
> return 0;
> }
>
> -static int zram_read_before_write(struct zram *zram, char *mem, u32 index)
> +static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> + u32 index, int offset, struct bio *bio)
> {
> int ret;
> - size_t clen = PAGE_SIZE;
> - unsigned char *cmem;
> - unsigned long handle = zram->table[index].handle;
> + struct page *page;
> + unsigned char *user_mem, *uncmem = NULL;
>
> - if (zram_test_flag(zram, index, ZRAM_ZERO) || !handle) {
> - memset(mem, 0, PAGE_SIZE);
> + page = bvec->bv_page;
> +
> + if (unlikely(!zram->table[index].handle) ||
> + zram_test_flag(zram, index, ZRAM_ZERO)) {
> + pr_debug("Read before write: sector=%lu, size=%u",
> + (ulong)(bio->bi_sector), bio->bi_size);
"Read before write" message is not valid in case ZRAM_ZERO flag is set.
Its true only in !handle case.
Otherwise, the patch looks good to me.
On a side note, zram still contains a known use-after-free bug reported
by Fengguang Wu (CC'ed) which happens in the "partial I/O" i.e. non
PAGE_SIZE'ed I/O case which is fixed by the following patch.
Please let me know if you can include the following patch when you
resend this patch series, or I can do the same or will wait for this to
be merged and then send it later.
======
zram: Fix use-after-free in partial I/O case
When the compressed size of a page exceeds a threshold, the page is
stored as-is i.e. in uncompressed form. In the partial I/O i.e.
non-PAGE_SIZE'ed I/O case, however, the uncompressed memory was being
freed before it could be copied into the zsmalloc pool resulting in
use-after-free bug.
Signed-off-by: Nitin Gupta <ngupta@...are.org>
---
diff --git a/drivers/staging/zram/zram_drv.c
b/drivers/staging/zram/zram_drv.c
index 7585467..635736b 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -288,10 +288,8 @@ 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;
- }
}
/*
@@ -312,8 +310,6 @@ static int zram_bvec_write(struct zram *zram, struct
bio_vec *bvec, u32 index,
if (page_zero_filled(uncmem)) {
kunmap_atomic(user_mem);
- if (is_partial_io(bvec))
- kfree(uncmem);
zram_stat_inc(&zram->stats.pages_zero);
zram_set_flag(zram, index, ZRAM_ZERO);
ret = 0;
@@ -324,8 +320,6 @@ static int zram_bvec_write(struct zram *zram, struct
bio_vec *bvec, u32 index,
zram->compress_workmem);
kunmap_atomic(user_mem);
- if (is_partial_io(bvec))
- kfree(uncmem);
if (unlikely(ret != LZO_E_OK)) {
pr_err("Compression failed! err=%d\n", ret);
@@ -360,11 +354,15 @@ 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;
+ ret = 0;
out:
if (ret)
zram_stat64_inc(zram, &zram->stats.failed_writes);
+
+ if (is_partial_io(bvec))
+ kfree(uncmem);
+
return ret;
}
BTW, I could not trigger this partial I/O case, so please let me know if
you hit any issue during your testing.
There is another sparse warning to be fixed: zram_reset_device should be
static.
Thanks,
Nitin
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