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dd(1): Enable access to SIZE_T_MAX character devices

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On machines where SIZE_T_MAX exceeds OFF_MAX (signed 64-bit), permit seeking
character devices to negative off_t values.  This enables dd(1) to interact
with kernel KVA in /dev/kmem on amd64, for example.

Sponsored by:	EMC / Isilon Storage Division
This commit is contained in:
Conrad Meyer 2016-07-09 17:11:54 +00:00
parent c266ab3830
commit b156d221c9
2 changed files with 31 additions and 10 deletions
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8
bin/dd/args.c
View File

@ -167,14 +167,6 @@ jcl(char **argv)
errx(1, "cbs meaningless if not doing record operations");
} else
cfunc = def;
/*
* Bail out if the calculation of a file offset would overflow.
*/
if (in.offset > OFF_MAX / (ssize_t)in.dbsz ||
out.offset > OFF_MAX / (ssize_t)out.dbsz)
errx(1, "seek offsets cannot be larger than %jd",
(intmax_t)OFF_MAX);
}
static int

33
bin/dd/position.c
View File

@ -45,12 +45,41 @@ __FBSDID("$FreeBSD$");
#include <err.h>
#include <errno.h>
#include <inttypes.h>
#include <limits.h>
#include <signal.h>
#include <unistd.h>
#include "dd.h"
#include "extern.h"
static off_t
seek_offset(IO *io)
{
off_t n;
size_t sz;
n = io->offset;
sz = io->dbsz;
_Static_assert(sizeof(io->offset) == sizeof(int64_t), "64-bit off_t");
/*
* If the lseek offset will be negative, verify that this is a special
* device file. Some such files (e.g. /dev/kmem) permit "negative"
* offsets.
*
* Bail out if the calculation of a file offset would overflow.
*/
if ((io->flags & ISCHR) == 0 && n > OFF_MAX / (ssize_t)sz)
errx(1, "seek offsets cannot be larger than %jd",
(intmax_t)OFF_MAX);
else if ((io->flags & ISCHR) != 0 && (uint64_t)n > UINT64_MAX / sz)
errx(1, "seek offsets cannot be larger than %ju",
(uintmax_t)UINT64_MAX);
return ((off_t)( (uint64_t)n * sz ));
}
/*
* Position input/output data streams before starting the copy. Device type
* dependent. Seekable devices use lseek, and the rest position by reading.
@ -68,7 +97,7 @@ pos_in(void)
/* If known to be seekable, try to seek on it. */
if (in.flags & ISSEEK) {
errno = 0;
if (lseek(in.fd, in.offset * in.dbsz, SEEK_CUR) == -1 &&
if (lseek(in.fd, seek_offset(&in), SEEK_CUR) == -1 &&
errno != 0)
err(1, "%s", in.name);
return;
@ -136,7 +165,7 @@ pos_out(void)
*/
if (out.flags & (ISSEEK | ISPIPE)) {
errno = 0;
if (lseek(out.fd, out.offset * out.dbsz, SEEK_CUR) == -1 &&
if (lseek(out.fd, seek_offset(&out), SEEK_CUR) == -1 &&
errno != 0)
err(1, "%s", out.name);
return;