Skip to main content

Browse the archive

https://github.com/torvalds/linux
23 October 2021, 00:29:24 UTC
Revision 86d32f9a7c54ad74f4514d7fef7c847883207291 authored by Vasily Averin on 14 April 2020, 20:33:16 UTC, committed by Linus Torvalds on 16 April 2020, 17:10:50 UTC 
keys: Fix proc_keys_next to increase position index
 
If seq_file .next function does not change position index,
read after some lseek can generate unexpected output:

    $ dd if=/proc/keys bs=1  # full usual output
    0f6bfdf5 I--Q---     2 perm 3f010000  1000  1000 user      4af2f79ab8848d0a: 740
    1fb91b32 I--Q---     3 perm 1f3f0000  1000 65534 keyring   _uid.1000: 2
    27589480 I--Q---     1 perm 0b0b0000     0     0 user      invocation_id: 16
    2f33ab67 I--Q---   152 perm 3f030000     0     0 keyring   _ses: 2
    33f1d8fa I--Q---     4 perm 3f030000  1000  1000 keyring   _ses: 1
    3d427fda I--Q---     2 perm 3f010000  1000  1000 user      69ec44aec7678e5a: 740
    3ead4096 I--Q---     1 perm 1f3f0000  1000 65534 keyring   _uid_ses.1000: 1
    521+0 records in
    521+0 records out
    521 bytes copied, 0,00123769 s, 421 kB/s

But a read after lseek in middle of last line results in the partial
last line and then a repeat of the final line:

    $ dd if=/proc/keys bs=500 skip=1
    dd: /proc/keys: cannot skip to specified offset
    g   _uid_ses.1000: 1
    3ead4096 I--Q---     1 perm 1f3f0000  1000 65534 keyring   _uid_ses.1000: 1
    0+1 records in
    0+1 records out
    97 bytes copied, 0,000135035 s, 718 kB/s

and a read after lseek beyond end of file results in the last line being
shown:

    $ dd if=/proc/keys bs=1000 skip=1   # read after lseek beyond end of file
    dd: /proc/keys: cannot skip to specified offset
    3ead4096 I--Q---     1 perm 1f3f0000  1000 65534 keyring   _uid_ses.1000: 1
    0+1 records in
    0+1 records out
    76 bytes copied, 0,000119981 s, 633 kB/s

See https://bugzilla.kernel.org/show_bug.cgi?id=206283

Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code ...")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent 0008633
Raw File
Tip revision: 86d32f9a7c54ad74f4514d7fef7c847883207291 authored by Vasily Averin on 14 April 2020, 20:33:16 UTC
keys: Fix proc_keys_next to increase position index
Tip revision: 86d32f9
kasprintf.c 
// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/lib/kasprintf.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <stdarg.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/string.h>

/* Simplified asprintf. */
char *kvasprintf(gfp_t gfp, const char *fmt, va_list ap)
{
	unsigned int first, second;
	char *p;
	va_list aq;

	va_copy(aq, ap);
	first = vsnprintf(NULL, 0, fmt, aq);
	va_end(aq);

	p = kmalloc_track_caller(first+1, gfp);
	if (!p)
		return NULL;

	second = vsnprintf(p, first+1, fmt, ap);
	WARN(first != second, "different return values (%u and %u) from vsnprintf(\"%s\", ...)",
	     first, second, fmt);

	return p;
}
EXPORT_SYMBOL(kvasprintf);

/*
 * If fmt contains no % (or is exactly %s), use kstrdup_const. If fmt
 * (or the sole vararg) points to rodata, we will then save a memory
 * allocation and string copy. In any case, the return value should be
 * freed using kfree_const().
 */
const char *kvasprintf_const(gfp_t gfp, const char *fmt, va_list ap)
{
	if (!strchr(fmt, '%'))
		return kstrdup_const(fmt, gfp);
	if (!strcmp(fmt, "%s"))
		return kstrdup_const(va_arg(ap, const char*), gfp);
	return kvasprintf(gfp, fmt, ap);
}
EXPORT_SYMBOL(kvasprintf_const);

char *kasprintf(gfp_t gfp, const char *fmt, ...)
{
	va_list ap;
	char *p;

	va_start(ap, fmt);
	p = kvasprintf(gfp, fmt, ap);
	va_end(ap);

	return p;
}
EXPORT_SYMBOL(kasprintf);
back to top