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xkb: Handle xkb formated string output safely (CVE-2017-13723)

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Generating strings for XKB data used a single shared static buffer,
which offered several opportunities for errors. Use a ring of
resizable buffers instead, to avoid problems when strings end up
longer than anticipated.

Reviewed-by: Michal Srb <msrb@suse.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Julien Cristau <jcristau@debian.org>
This commit is contained in:
Keith Packard
2017-07-27 10:08:32 -07:00
committed by Julien Cristau
parent eaf1f72ed8
commit 94f11ca5cf
1 changed files with 20 additions and 20 deletions
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40
xkb/xkbtext.c
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@@ -47,23 +47,27 @@
/***====================================================================***/
#define BUFFER_SIZE 512
static char textBuffer[BUFFER_SIZE];
static int tbNext = 0;
#define NUM_BUFFER 8
static struct textBuffer {
int size;
char *buffer;
} textBuffer[NUM_BUFFER];
static int textBufferIndex;
static char *
tbGetBuffer(unsigned size)
{
char *rtrn;
struct textBuffer *tb;
if (size >= BUFFER_SIZE)
return NULL;
if ((BUFFER_SIZE - tbNext) <= size)
tbNext = 0;
rtrn = &textBuffer[tbNext];
tbNext += size;
return rtrn;
tb = &textBuffer[textBufferIndex];
textBufferIndex = (textBufferIndex + 1) % NUM_BUFFER;
if (size > tb->size) {
free(tb->buffer);
tb->buffer = xnfalloc(size);
tb->size = size;
}
return tb->buffer;
}
/***====================================================================***/
@@ -79,8 +83,6 @@ XkbAtomText(Atom atm, unsigned format)
int len;
len = strlen(atmstr) + 1;
if (len > BUFFER_SIZE)
len = BUFFER_SIZE - 2;
rtrn = tbGetBuffer(len);
strlcpy(rtrn, atmstr, len);
}
@@ -128,8 +130,6 @@ XkbVModIndexText(XkbDescPtr xkb, unsigned ndx, unsigned format)
len = strlen(tmp) + 1;
if (format == XkbCFile)
len += 4;
if (len >= BUFFER_SIZE)
len = BUFFER_SIZE - 1;
rtrn = tbGetBuffer(len);
if (format == XkbCFile) {
strcpy(rtrn, "vmod_");
@@ -140,6 +140,8 @@ XkbVModIndexText(XkbDescPtr xkb, unsigned ndx, unsigned format)
return rtrn;
}
#define VMOD_BUFFER_SIZE 512
char *
XkbVModMaskText(XkbDescPtr xkb,
unsigned modMask, unsigned mask, unsigned format)
@@ -147,7 +149,7 @@ XkbVModMaskText(XkbDescPtr xkb,
register int i, bit;
int len;
char *mm, *rtrn;
char *str, buf[BUFFER_SIZE];
char *str, buf[VMOD_BUFFER_SIZE];
if ((modMask == 0) && (mask == 0)) {
rtrn = tbGetBuffer(5);
@@ -173,7 +175,7 @@ XkbVModMaskText(XkbDescPtr xkb,
len = strlen(tmp) + 1 + (str == buf ? 0 : 1);
if (format == XkbCFile)
len += 4;
if ((str - (buf + len)) <= BUFFER_SIZE) {
if ((str - (buf + len)) <= VMOD_BUFFER_SIZE) {
if (str != buf) {
if (format == XkbCFile)
*str++ = '|';
@@ -199,8 +201,6 @@ XkbVModMaskText(XkbDescPtr xkb,
len = 0;
if (str)
len += strlen(str) + (mm == NULL ? 0 : 1);
if (len >= BUFFER_SIZE)
len = BUFFER_SIZE - 1;
rtrn = tbGetBuffer(len + 1);
rtrn[0] = '\0';