picnoir/Systemd
1
0
Fork 0
Code Issues Pull requests Projects Releases Wiki Activity

libsystemd-network: make option_append() atomic and make the code a bit clearer

Browse source 
Comparisons are done in the normal order (if (need > available), not if (available < need)),
variables have reduced scope and are renamed for clarity.

The only functional change is that if we return -ENAMETOOLONG, we do that
without modifying the options[] array.

I also added an explanatory comment. The use of one offset to point into three
buffers is not obvious.

Coverity (in CID#1402354) says that sname might be accessed at bad offset, but
I cannot see this happening. We check for available space before writing anything.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2019-08-03 16:49:39 +02:00
parent 10b1d42e57
commit bc67342e94
1 changed files with 35 additions and 30 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

65
src/libsystemd-network/dhcp-option.c
View file

@ -27,7 +27,7 @@ static int option_append(uint8_t options[], size_t size, size_t *offset,
case SD_DHCP_OPTION_PAD:
case SD_DHCP_OPTION_END:
if (size < *offset + 1)
if (*offset + 1 > size)
return -ENOBUFS;
options[*offset] = code;
@ -35,42 +35,45 @@ static int option_append(uint8_t options[], size_t size, size_t *offset,
break;
case SD_DHCP_OPTION_USER_CLASS: {
size_t len = 0;
size_t total = 0;
char **s;
STRV_FOREACH(s, (char **) optval)
len += strlen(*s) + 1;
if (size < *offset + len + 2)
return -ENOBUFS;
options[*offset] = code;
options[*offset + 1] = len;
*offset += 2;
STRV_FOREACH(s, (char **) optval) {
len = strlen(*s);
size_t len = strlen(*s);
if (len > 255)
return -ENAMETOOLONG;
total += 1 + len;
}
if (*offset + 2 + total > size)
return -ENOBUFS;
options[*offset] = code;
options[*offset + 1] = total;
*offset += 2;
STRV_FOREACH(s, (char **) optval) {
size_t len = strlen(*s);
options[*offset] = len;
memcpy_safe(&options[*offset + 1], *s, len);
*offset += len + 1;
memcpy(&options[*offset + 1], *s, len);
*offset += 1 + len;
}
break;
}
default:
if (size < *offset + optlen + 2)
if (*offset + 2 + optlen > size)
return -ENOBUFS;
options[*offset] = code;
options[*offset + 1] = optlen;
memcpy_safe(&options[*offset + 2], optval, optlen);
*offset += optlen + 2;
*offset += 2 + optlen;
break;
}
@ -81,22 +84,25 @@ static int option_append(uint8_t options[], size_t size, size_t *offset,
int dhcp_option_append(DHCPMessage *message, size_t size, size_t *offset,
uint8_t overload,
uint8_t code, size_t optlen, const void *optval) {
size_t file_offset = 0, sname_offset =0;
bool file, sname;
const bool use_file = overload & DHCP_OVERLOAD_FILE;
const bool use_sname = overload & DHCP_OVERLOAD_SNAME;
int r;
assert(message);
assert(offset);
file = overload & DHCP_OVERLOAD_FILE;
sname = overload & DHCP_OVERLOAD_SNAME;
/* If *offset is in range [0, size), we are writing to ->options,
* if *offset is in range [size, size + sizeof(message->file)) and use_file, we are writing to ->file,
* if *offset is in range [size + use_file*sizeof(message->file), size + use_file*sizeof(message->file) + sizeof(message->sname))
* and use_sname, we are writing to ->sname.
*/
if (*offset < size) {
/* still space in the options array */
r = option_append(message->options, size, offset, code, optlen, optval);
if (r >= 0)
return 0;
else if (r == -ENOBUFS && (file || sname)) {
else if (r == -ENOBUFS && (use_file || use_sname)) {
/* did not fit, but we have more buffers to try
close the options array and move the offset to its end */
r = option_append(message->options, size, offset, SD_DHCP_OPTION_END, 0, NULL);
@ -108,8 +114,8 @@ int dhcp_option_append(DHCPMessage *message, size_t size, size_t *offset,
return r;
}
if (overload & DHCP_OVERLOAD_FILE) {
file_offset = *offset - size;
if (use_file) {
size_t file_offset = *offset - size;
if (file_offset < sizeof(message->file)) {
/* still space in the 'file' array */
@ -117,7 +123,7 @@ int dhcp_option_append(DHCPMessage *message, size_t size, size_t *offset,
if (r >= 0) {
*offset = size + file_offset;
return 0;
} else if (r == -ENOBUFS && sname) {
} else if (r == -ENOBUFS && use_sname) {
/* did not fit, but we have more buffers to try
close the file array and move the offset to its end */
r = option_append(message->options, size, offset, SD_DHCP_OPTION_END, 0, NULL);
@ -130,19 +136,18 @@ int dhcp_option_append(DHCPMessage *message, size_t size, size_t *offset,
}
}
if (overload & DHCP_OVERLOAD_SNAME) {
sname_offset = *offset - size - (file ? sizeof(message->file) : 0);
if (use_sname) {
size_t sname_offset = *offset - size - use_file*sizeof(message->file);
if (sname_offset < sizeof(message->sname)) {
/* still space in the 'sname' array */
r = option_append(message->sname, sizeof(message->sname), &sname_offset, code, optlen, optval);
if (r >= 0) {
*offset = size + (file ? sizeof(message->file) : 0) + sname_offset;
*offset = size + use_file*sizeof(message->file) + sname_offset;
return 0;
} else {
} else
/* no space, or other error, give up */
return r;
}
}
}