[PATCH v7 2/7] pcapng: use malloc instead of fixed buffer size

Stephen Hemminger
2026-02-13T19:20:58Z

The administrative APIs accept comments and other metadata as
strings. Since these strings can be arbitrarily long (up to
UINT16_MAX bytes), they may overflow the fixed-size stack buffers
previously used for block construction.

Replace the fixed-size buffers with dynamically allocated memory
sized to the actual block length. Return appropriate error codes
on allocation failure.

Bugzilla ID: 1820
Fixes: 8d23ce8f5ee9 ("pcapng: add new library for writing pcapng files")
Cc: stable@dpdk.org

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
lib/pcapng/rte_pcapng.c | 44 ++++++++++++++++++++++++++---------------
lib/pcapng/rte_pcapng.h | 1 +
2 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/lib/pcapng/rte_pcapng.c b/lib/pcapng/rte_pcapng.c
index 4ccf833777..413e6f1f4a 100644
--- a/lib/pcapng/rte_pcapng.c
+++ b/lib/pcapng/rte_pcapng.c
@@ -37,9 +37,6 @@
/* upper bound for strings in pcapng option data */
#define PCAPNG_STR_MAX UINT16_MAX

-/* upper bound for section, stats and interface blocks (in uint32_t) */
-#define PCAPNG_BLKSIZ (2048 / sizeof(uint32_t))
-
/* Format of the capture file handle */
struct rte_pcapng {
int outfd; /* output file */
@@ -148,8 +145,9 @@ pcapng_section_block(rte_pcapng_t *self,
{
struct pcapng_section_header *hdr;
struct pcapng_option *opt;
- uint32_t buf[PCAPNG_BLKSIZ];
+ uint32_t *buf;
uint32_t len;
+ ssize_t ret;

len = sizeof(*hdr);
if (hw)
@@ -165,8 +163,9 @@ pcapng_section_block(rte_pcapng_t *self,
len += pcapng_optlen(0);
len += sizeof(uint32_t);

- if (len > sizeof(buf))
- return -1;
+ buf = malloc(len);
+ if (buf == NULL)
+ return -ENOMEM;

hdr = (struct pcapng_section_header *)buf;
*hdr = (struct pcapng_section_header) {
@@ -199,7 +198,9 @@ pcapng_section_block(rte_pcapng_t *self,
/* clone block_length after option */
memcpy(opt, &hdr->block_length, sizeof(uint32_t));

- return write(self->outfd, buf, len);
+ ret = write(self->outfd, buf, len);
+ free(buf);
+ return ret < 0 ? -errno : 0;
}

/* Write an interface block for a DPDK port */
@@ -217,7 +218,7 @@ rte_pcapng_add_interface(rte_pcapng_t *self, uint16_t port, uint16_t link_type,
struct pcapng_option *opt;
const uint8_t tsresol = 9; /* nanosecond resolution */
uint32_t len;
- uint32_t buf[PCAPNG_BLKSIZ];
+ uint32_t *buf;
char ifname_buf[IF_NAMESIZE];
char ifhw[256];
uint64_t speed = 0;
@@ -279,8 +280,9 @@ rte_pcapng_add_interface(rte_pcapng_t *self, uint16_t port, uint16_t link_type,
len += pcapng_optlen(0);
len += sizeof(uint32_t);

- if (len > sizeof(buf))
- return -EINVAL;
+ buf = malloc(len);
+ if (buf == NULL)
+ return -ENOMEM;

hdr = (struct pcapng_interface_block *)buf;
*hdr = (struct pcapng_interface_block) {
@@ -326,7 +328,9 @@ rte_pcapng_add_interface(rte_pcapng_t *self, uint16_t port, uint16_t link_type,
/* remember the file index */
self->port_index[port] = self->ports++;

- return write(self->outfd, buf, len);
+ ret = write(self->outfd, buf, len);
+ free(buf);
+ return ret;
}

/*
@@ -343,7 +347,8 @@ rte_pcapng_write_stats(rte_pcapng_t *self, uint16_t port_id,
uint64_t start_time = self->offset_ns;
uint64_t sample_time;
uint32_t optlen, len;
- uint32_t buf[PCAPNG_BLKSIZ];
+ uint32_t *buf;
+ ssize_t ret;

RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);

@@ -366,8 +371,9 @@ rte_pcapng_write_stats(rte_pcapng_t *self, uint16_t port_id,
optlen += pcapng_optlen(0);

len = sizeof(*hdr) + optlen + sizeof(uint32_t);
- if (len > sizeof(buf))
- return -1;
+ buf = malloc(len);
+ if (buf == NULL)
+ return -ENOMEM;

hdr = (struct pcapng_statistics *)buf;
opt = (struct pcapng_option *)(hdr + 1);
@@ -398,7 +404,9 @@ rte_pcapng_write_stats(rte_pcapng_t *self, uint16_t port_id,
/* clone block_length after option */
memcpy(opt, &len, sizeof(uint32_t));

- return write(self->outfd, buf, len);
+ ret = write(self->outfd, buf, len);
+ free(buf);
+ return ret;
}

RTE_EXPORT_SYMBOL(rte_pcapng_mbuf_size)
@@ -712,6 +720,7 @@ rte_pcapng_fdopen(int fd,
rte_pcapng_t *self;
struct timespec ts;
uint64_t cycles;
+ int ret;

if ((osname && strlen(osname) > PCAPNG_STR_MAX) ||
(hardware && strlen(hardware) > PCAPNG_STR_MAX) ||
@@ -739,8 +748,11 @@ rte_pcapng_fdopen(int fd,
for (i = 0; i < RTE_MAX_ETHPORTS; i++)
self->port_index[i] = UINT32_MAX;

- if (pcapng_section_block(self, osname, hardware, appname, comment) < 0)
+ ret = pcapng_section_block(self, osname, hardware, appname, comment);
+ if (ret < 0) {
+ rte_errno = -ret;
goto fail;
+ }

return self;
fail:
diff --git a/lib/pcapng/rte_pcapng.h b/lib/pcapng/rte_pcapng.h
index 2dd438842d..ff39fa7b49 100644
--- a/lib/pcapng/rte_pcapng.h
+++ b/lib/pcapng/rte_pcapng.h
@@ -200,6 +200,7 @@ rte_pcapng_write_packets(rte_pcapng_t *self,
* -1 on failure to write file (and errno is set)
* - (-ENODEV) if *port_id* is invalid.
* - (-EINVAL) if bad parameter
+ * - (-ENOMEM) could not allocate memory for buffer
*/
ssize_t
rte_pcapng_write_stats(rte_pcapng_t *self, uint16_t port,
--
2.51.0