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Commit e0a1a017 authored by Alexey Dobriyan's avatar Alexey Dobriyan Committed by Greg Kroah-Hartman
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proc: fix /proc/*/map_files lookup 

[ Upstream commit ac7f1061c2c11bb8936b1b6a94cdb48de732f7a4 ]

Current code does:

	if (sscanf(dentry->d_name.name, "%lx-%lx", start, end) != 2)

However sscanf() is broken garbage.

It silently accepts whitespace between format specifiers
(did you know that?).

It silently accepts valid strings which result in integer overflow.

Do not use sscanf() for any even remotely reliable parsing code.

	OK
	# readlink '/proc/1/map_files/55a23af39000-55a23b05b000'
	/lib/systemd/systemd

	broken
	# readlink '/proc/1/map_files/               55a23af39000-55a23b05b000'
	/lib/systemd/systemd

	broken
	# readlink '/proc/1/map_files/55a23af39000-55a23b05b000    '
	/lib/systemd/systemd

	very broken
	# readlink '/proc/1/map_files/1000000000000000055a23af39000-55a23b05b000'
	/lib/systemd/systemd

Andrei said:

: This patch breaks criu.  It was a bug in criu.  And this bug is on a minor
: path, which works when memfd_create() isn't available.  It is a reason why
: I ask to not backport this patch to stable kernels.
:
: In CRIU this bug can be triggered, only if this patch will be backported
: to a kernel which version is lower than v3.16.

Link: http://lkml.kernel.org/r/20171120212706.GA14325@avx2


Signed-off-by: default avatarAlexey Dobriyan <adobriyan@gmail.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarSasha Levin <alexander.levin@microsoft.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 0675ec13

fs/proc/base.c

+28 −1
Original line number Diff line number Diff line
@@ -94,6 +94,8 @@ 
#include "internal.h"

#include "fd.h"



#include "../../lib/kstrtox.h"



/* NOTE:

 *	Implementing inode permission operations in /proc is almost

 *	certainly an error.  Permission checks need to happen during
@@ -1864,8 +1866,33 @@ bool proc_fill_cache(struct file *file, struct dir_context *ctx, 
static int dname_to_vma_addr(struct dentry *dentry,

			     unsigned long *start, unsigned long *end)

{

	if (sscanf(dentry->d_name.name, "%lx-%lx", start, end) != 2)

	const char *str = dentry->d_name.name;

	unsigned long long sval, eval;

	unsigned int len;



	len = _parse_integer(str, 16, &sval);

	if (len & KSTRTOX_OVERFLOW)

		return -EINVAL;

	if (sval != (unsigned long)sval)

		return -EINVAL;

	str += len;



	if (*str != '-')

		return -EINVAL;

	str++;



	len = _parse_integer(str, 16, &eval);

	if (len & KSTRTOX_OVERFLOW)

		return -EINVAL;

	if (eval != (unsigned long)eval)

		return -EINVAL;

	str += len;



	if (*str != '\0')

		return -EINVAL;



	*start = sval;

	*end = eval;



	return 0;

}