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authorcperciva <cperciva@FreeBSD.org>2010-01-10 14:30:30 +0000
committercperciva <cperciva@FreeBSD.org>2010-01-10 14:30:30 +0000
commit030d49b206a72052b076bdf444707e89b797b324 (patch)
treee83a1bc4cb465b204318f65cb4f56fac5a48eddf /lib/libc/stdio/fread.c
parent8458b2914ed6f17f3f78f102fa4ea087cb4ffc67 (diff)
downloadFreeBSD-src-030d49b206a72052b076bdf444707e89b797b324.zip
FreeBSD-src-030d49b206a72052b076bdf444707e89b797b324.tar.gz
Give a less silly response to a silly request.
Prior to this commit, fread/fwrite calls with size * nmemb > SIZE_MAX were handled by reading or writing (size_t)(size * nmemb) bytes; for example, on 32-bit platforms, fread(ptr, 641, 6700417, f) would read 1 byte and indicate that the requested 6700417 blocks had been read. This commit adds a check for such integer overflows, and treats them as if an overly large request was passed to read/write; i.e., it sets errno to EINVAL, sets the error indicator on the file, and returns a short object count (0, to be specific). The overflow check involves an integer division, so as a performance optimization we check first to see if both size and nmemb are less than 2^16; if they are, no overflow is possible and we avoid the division. We assume here that size_t is at least 32 bits; this appears to be true on all platforms FreeBSD supports. Although this commit fixes an integer overflow, it is not likely to have any security implications, since any program which would be affected by this bug fix is quite clearly already very confused. Reviewed by: kib MFC after: 1 month
Diffstat (limited to 'lib/libc/stdio/fread.c')
-rw-r--r--lib/libc/stdio/fread.c23
1 files changed, 22 insertions, 1 deletions
diff --git a/lib/libc/stdio/fread.c b/lib/libc/stdio/fread.c
index 6253856..ad3ea29 100644
--- a/lib/libc/stdio/fread.c
+++ b/lib/libc/stdio/fread.c
@@ -37,6 +37,8 @@ static char sccsid[] = "@(#)fread.c 8.2 (Berkeley) 12/11/93";
__FBSDID("$FreeBSD$");
#include "namespace.h"
+#include <errno.h>
+#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include "un-namespace.h"
@@ -69,8 +71,27 @@ __fread(void * __restrict buf, size_t size, size_t count, FILE * __restrict fp)
/*
* ANSI and SUSv2 require a return value of 0 if size or count are 0.
*/
- if ((resid = count * size) == 0)
+ if ((count == 0) || (size == 0))
return (0);
+
+ /*
+ * Check for integer overflow. As an optimization, first check that
+ * at least one of {count, size} is at least 2^16, since if both
+ * values are less than that, their product can't possible overflow
+ * (size_t is always at least 32 bits on FreeBSD).
+ */
+ if (((count | size) > 0xFFFF) &&
+ (count > SIZE_MAX / size)) {
+ errno = EINVAL;
+ fp->_flags |= __SERR;
+ return (0);
+ }
+
+ /*
+ * Compute the (now required to not overflow) number of bytes to
+ * read and actually do the work.
+ */
+ resid = count * size;
ORIENT(fp, -1);
if (fp->_r < 0)
fp->_r = 0;
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