Re: [PATCH] RDMA/ocrdma: Fix an off-by-one issue in 'ocrdma_add_stat'

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 




Le 14/04/2020 à 20:34, Jason Gunthorpe a écrit :
On Sat, Mar 28, 2020 at 08:30:40AM +0100, Christophe JAILLET wrote:
There is an off-by-one issue when checking if there is enough space in the
output buffer, because we must keep some place for a final '\0'.

While at it:
    - Use 'scnprintf' instead of 'snprintf' in order to avoid a superfluous
     'strlen'
    - avoid some useless initializations
    - avoida hard coded buffer size that can be computed at built time.

Fixes: a51f06e1679e ("RDMA/ocrdma: Query controller information")
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
---
The '\0' comes from memset(..., 0, ...) in all callers.
This could be also avoided if needed.
---
  drivers/infiniband/hw/ocrdma/ocrdma_stats.c | 9 ++++-----
  1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/hw/ocrdma/ocrdma_stats.c b/drivers/infiniband/hw/ocrdma/ocrdma_stats.c
index 5f831e3bdbad..614a449e6b87 100644
--- a/drivers/infiniband/hw/ocrdma/ocrdma_stats.c
+++ b/drivers/infiniband/hw/ocrdma/ocrdma_stats.c
@@ -49,13 +49,12 @@ static struct dentry *ocrdma_dbgfs_dir;
  static int ocrdma_add_stat(char *start, char *pcur,
  				char *name, u64 count)
  {
-	char buff[128] = {0};
-	int cpy_len = 0;
+	char buff[128];
+	int cpy_len;
- snprintf(buff, 128, "%s: %llu\n", name, count);
-	cpy_len = strlen(buff);
+	cpy_len = scnprintf(buff, sizeof(buff), "%s: %llu\n", name, count);
- if (pcur + cpy_len > start + OCRDMA_MAX_DBGFS_MEM) {
+	if (pcur + cpy_len >= start + OCRDMA_MAX_DBGFS_MEM) {
  		pr_err("%s: No space in stats buff\n", __func__);
  		return 0;
  	}
The memcpy is still kind of silly right? What about this:

static int ocrdma_add_stat(char *start, char *pcur, char *name, u64 count)
{
	size_t len = (start + OCRDMA_MAX_DBGFS_MEM) - pcur;
	int cpy_len;

	cpy_len = snprintf(pcur, len, "%s: %llu\n", name, count);
	if (cpy_len >= len || cpy_len < 0) {
		pr_err("%s: No space in stats buff\n", __func__);
		return 0;
	}
	return cpy_len;
}

Jason

It can looks useless, but I think that the goal was to make sure that we would not display truncated data. Each line is either complete or absent.

I don't have any strong opinion of what is best, but I can understand the current logic.

This function is not a hot spot, so useless memcpy is not a big issue.

CJ





[Index of Archives]     [Kernel Development]     [Kernel Announce]     [Kernel Newbies]     [Linux Networking Development]     [Share Photos]     [IDE]     [Security]     [Git]     [Netfilter]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Device Mapper]

  Powered by Linux