[PATCH v2] nfc: pn533: Fix double free when pn533_fill_fragment_skbs() fails

skb is already freed by dev_kfree_skb in pn533_fill_fragment_skbs,
but follow error handler branch when pn533_fill_fragment_skbs()
fails, skb is freed again, results in double free issue. Fix this
by not free skb in error path of pn533_fill_fragment_skbs.

Signed-off-by: Chengfeng Ye <redacted>
---
 drivers/nfc/pn533/pn533.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/nfc/pn533/pn533.c b/drivers/nfc/pn533/pn533.c
index 787bcbd290f7..a491db46e3bd 100644
--- a/drivers/nfc/pn533/pn533.c
+++ b/drivers/nfc/pn533/pn533.c

@@ -2216,7 +2216,7 @@ static int pn533_fill_fragment_skbs(struct pn533 *dev, struct sk_buff *skb)
 		frag = pn533_alloc_skb(dev, frag_size);
 		if (!frag) {
 			skb_queue_purge(&dev->fragment_skb);
-			break;
+			return -ENOMEM;
 		}
 
 		if (!dev->tgt_mode) {

@@ -2285,7 +2285,7 @@ static int pn533_transceive(struct nfc_dev *nfc_dev,
 		/* jumbo frame ? */
 		if (skb->len > PN533_CMD_DATAEXCH_DATA_MAXLEN) {
 			rc = pn533_fill_fragment_skbs(dev, skb);
-			if (rc <= 0)
+			if (rc < 0)
 				goto error;
 
 			skb = skb_dequeue(&dev->fragment_skb);

@@ -2353,7 +2353,7 @@ static int pn533_tm_send(struct nfc_dev *nfc_dev, struct sk_buff *skb)
 	/* let's split in multiple chunks if size's too big */
 	if (skb->len > PN533_CMD_DATAEXCH_DATA_MAXLEN) {
 		rc = pn533_fill_fragment_skbs(dev, skb);
-		if (rc <= 0)
+		if (rc < 0)
 			goto error;
 
 		/* get the first skb */

-- 
2.17.1

On Fri, Nov 05, 2021 at 06:36:36AM -0700, Chengfeng Ye wrote:

skb is already freed by dev_kfree_skb in pn533_fill_fragment_skbs,
but follow error handler branch when pn533_fill_fragment_skbs()
fails, skb is freed again, results in double free issue. Fix this
by not free skb in error path of pn533_fill_fragment_skbs.

Signed-off-by: Chengfeng Ye <redacted>

I sort of wish the commit message talked more about the how this changes
the failure return from 0 to -ENOMEM.  But the patch is good.

Reviewed-by: Dan Carpenter <redacted>

regards,
dan carpenter

On 05/11/2021 14:36, Chengfeng Ye wrote:

skb is already freed by dev_kfree_skb in pn533_fill_fragment_skbs,
but follow error handler branch when pn533_fill_fragment_skbs()
fails, skb is freed again, results in double free issue. Fix this
by not free skb in error path of pn533_fill_fragment_skbs.

Signed-off-by: Chengfeng Ye <redacted>
---
 drivers/nfc/pn533/pn533.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Looks good, thanks:
Reviewed-by: Krzysztof Kozlowski <redacted>

Please do not forget about fixes tag. Here it is trickier because
pn533_fill_fragment_skbs() usage was introduced in two commits:

Fixes: 963a82e07d4e ("NFC: pn533: Split large Tx frames in chunks")
Fixes: 93ad42020c2d ("NFC: pn533: Target mode Tx fragmentation support")
Cc: <redacted>

Best regards,
Krzysztof

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller [off-list ref]:

On Fri,  5 Nov 2021 06:36:36 -0700 you wrote:

skb is already freed by dev_kfree_skb in pn533_fill_fragment_skbs,
but follow error handler branch when pn533_fill_fragment_skbs()
fails, skb is freed again, results in double free issue. Fix this
by not free skb in error path of pn533_fill_fragment_skbs.

Signed-off-by: Chengfeng Ye <redacted>

[...]

Here is the summary with links:
  - [v2] nfc: pn533: Fix double free when pn533_fill_fragment_skbs() fails
    https://git.kernel.org/netdev/net/c/9fec40f85065

You are awesome, thank you!
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