wirtev: Get rid of alloca
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Commit Message
Use a scratch_buffer rather than alloca to avoid potential stack
overflows.
---
sysdeps/posix/writev.c | 35 ++++++++++++-----------------------
1 file changed, 12 insertions(+), 23 deletions(-)
Comments
On Thu, Jun 08, 2023 at 11:52:14AM -0400, Joe Simmons-Talbott wrote:
> Use a scratch_buffer rather than alloca to avoid potential stack
> overflows.
Please disregard this patch. There's a typo in the subject so I'll send
a new patch with that fixed.
Thanks,
Joe
> ---
> sysdeps/posix/writev.c | 35 ++++++++++++-----------------------
> 1 file changed, 12 insertions(+), 23 deletions(-)
>
> diff --git a/sysdeps/posix/writev.c b/sysdeps/posix/writev.c
> index 53e090c087..0cee0aa692 100644
> --- a/sysdeps/posix/writev.c
> +++ b/sysdeps/posix/writev.c
> @@ -19,19 +19,13 @@
> #include <unistd.h>
> #include <string.h>
> #include <limits.h>
> +#include <scratch_buffer.h>
> #include <stdbool.h>
> #include <sys/param.h>
> #include <sys/uio.h>
> #include <errno.h>
>
>
> -static void
> -ifree (char **ptrp)
> -{
> - free (*ptrp);
> -}
> -
> -
> /* Write data pointed by the buffers described by VECTOR, which
> is a vector of COUNT 'struct iovec's, to file descriptor FD.
> The data is written in the order specified.
> @@ -53,22 +47,15 @@ __writev (int fd, const struct iovec *vector, int count)
> bytes += vector[i].iov_len;
> }
>
> - /* Allocate a temporary buffer to hold the data. We should normally
> - use alloca since it's faster and does not require synchronization
> - with other threads. But we cannot if the amount of memory
> - required is too large. */
> - char *buffer;
> - char *malloced_buffer __attribute__ ((__cleanup__ (ifree))) = NULL;
> - if (__libc_use_alloca (bytes))
> - buffer = (char *) __alloca (bytes);
> - else
> - {
> - malloced_buffer = buffer = (char *) malloc (bytes);
> - if (buffer == NULL)
> - /* XXX I don't know whether it is acceptable to try writing
> - the data in chunks. Probably not so we just fail here. */
> - return -1;
> - }
> + /* Allocate a temporary buffer to hold the data. Use a scratch_buffer
> + since it's faster for small buffer sizes but can handle larger
> + allocations as well. */
> +
> + struct scratch_buffer buf;
> + scratch_buffer_init (&buf);
> + if (!scratch_buffer_set_array_size (&buf, 1, bytes))
> + return -1;
> + char *buffer = buf.data;
>
> /* Copy the data into BUFFER. */
> size_t to_copy = bytes;
> @@ -86,6 +73,8 @@ __writev (int fd, const struct iovec *vector, int count)
>
> ssize_t bytes_written = __write (fd, buffer, bytes);
>
> + scratch_buffer_free (&buf);
> +
> return bytes_written;
> }
> libc_hidden_def (__writev)
> --
> 2.39.2
>
@@ -19,19 +19,13 @@
#include <unistd.h>
#include <string.h>
#include <limits.h>
+#include <scratch_buffer.h>
#include <stdbool.h>
#include <sys/param.h>
#include <sys/uio.h>
#include <errno.h>
-static void
-ifree (char **ptrp)
-{
- free (*ptrp);
-}
-
-
/* Write data pointed by the buffers described by VECTOR, which
is a vector of COUNT 'struct iovec's, to file descriptor FD.
The data is written in the order specified.
@@ -53,22 +47,15 @@ __writev (int fd, const struct iovec *vector, int count)
bytes += vector[i].iov_len;
}
- /* Allocate a temporary buffer to hold the data. We should normally
- use alloca since it's faster and does not require synchronization
- with other threads. But we cannot if the amount of memory
- required is too large. */
- char *buffer;
- char *malloced_buffer __attribute__ ((__cleanup__ (ifree))) = NULL;
- if (__libc_use_alloca (bytes))
- buffer = (char *) __alloca (bytes);
- else
- {
- malloced_buffer = buffer = (char *) malloc (bytes);
- if (buffer == NULL)
- /* XXX I don't know whether it is acceptable to try writing
- the data in chunks. Probably not so we just fail here. */
- return -1;
- }
+ /* Allocate a temporary buffer to hold the data. Use a scratch_buffer
+ since it's faster for small buffer sizes but can handle larger
+ allocations as well. */
+
+ struct scratch_buffer buf;
+ scratch_buffer_init (&buf);
+ if (!scratch_buffer_set_array_size (&buf, 1, bytes))
+ return -1;
+ char *buffer = buf.data;
/* Copy the data into BUFFER. */
size_t to_copy = bytes;
@@ -86,6 +73,8 @@ __writev (int fd, const struct iovec *vector, int count)
ssize_t bytes_written = __write (fd, buffer, bytes);
+ scratch_buffer_free (&buf);
+
return bytes_written;
}
libc_hidden_def (__writev)