posix: Fix generic p{read,write}v buffer allocation (BZ#22457)

As described in BZ#22457 an interpose malloc can free an invalid
pointer for fallback preadv implementation.  Fortunately this is
just and issue on microblaze-linux-gnu running kernels older than
3.15.  This patch fixes it by calling mmap/unmap instead of
posix_memalign/ free.

Checked on microblaze-linux-gnu check with run-built-tests=no and
by using the sysdeps/posix implementation on x86_64-linux-gnu (just
for sanity test where it shown no regression).

	[BZ #22457]
	* sysdeps/posix/preadv_common.c (PREADV): Use mmap/munmap instead of
	posix_memalign/free.
	* sysdeps/posix/pwritev_common.c (PWRITEV): Likewise.

2 files changed, 10 insertions, 6 deletions

diff --git a/sysdeps/posix/preadv_common.c b/sysdeps/posix/preadv_common.c
index 37efdc0..76cf261 100644
--- a/sysdeps/posix/preadv_common.c
+++ b/sysdeps/posix/preadv_common.c
@@ -24,6 +24,7 @@
 #include <malloc.h>
 
 #include <ldsodefs.h>
+#include <libc-pointer-arith.h>
 
 /* Read data from file descriptor FD at the given position OFFSET
    without change the file pointer, and put the result in the buffers
@@ -54,8 +55,9 @@ PREADV (int fd, const struct iovec *vector, int count, OFF_T offset)
      but 1. it is system specific (not meant in generic implementation), and
      2. it would make the implementation more complex, and 3. it will require
      another syscall (fcntl).  */
-  void *buffer = NULL;
-  if (__posix_memalign (&buffer, GLRO(dl_pagesize), bytes) != 0)
+  void *buffer = __mmap (NULL, bytes, PROT_READ | PROT_WRITE,
+		         MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (__glibc_unlikely (buffer == MAP_FAILED))
     return -1;
 
   ssize_t bytes_read = PREAD (fd, buffer, bytes, offset);
@@ -78,6 +80,6 @@ PREADV (int fd, const struct iovec *vector, int count, OFF_T offset)
     }
 
 end:
-  free (buffer);
+  __munmap (buffer, bytes);
   return bytes_read;
 }
diff --git a/sysdeps/posix/pwritev_common.c b/sysdeps/posix/pwritev_common.c
index 0383065..3528fd8 100644
--- a/sysdeps/posix/pwritev_common.c
+++ b/sysdeps/posix/pwritev_common.c
@@ -24,6 +24,7 @@
 #include <malloc.h>
 
 #include <ldsodefs.h>
+#include <libc-pointer-arith.h>
 
 /* Write data pointed by the buffers described by IOVEC, which is a
    vector of COUNT 'struct iovec's, to file descriptor FD at the given
@@ -54,8 +55,9 @@ PWRITEV (int fd, const struct iovec *vector, int count, OFF_T offset)
      but 1. it is system specific (not meant in generic implementation), and
      2. it would make the implementation more complex, and 3. it will require
      another syscall (fcntl).  */
-  void *buffer = NULL;
-  if (__posix_memalign (&buffer, GLRO(dl_pagesize), bytes) != 0)
+  void *buffer = __mmap (NULL, bytes, PROT_WRITE,
+		         MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (__glibc_unlikely (buffer == MAP_FAILED))
     return -1;
 
   /* Copy the data from BUFFER into the memory specified by VECTOR.  */
@@ -66,7 +68,7 @@ PWRITEV (int fd, const struct iovec *vector, int count, OFF_T offset)
 
   ssize_t ret = PWRITE (fd, buffer, bytes, offset);
 
-  free (buffer);
+  __munmap (buffer, bytes);
 
   return ret;
 }