Re: [libvirt] [PATCH] phyp: Fixing possible buffer overflow

On 07/15/2010 06:37 PM, Eduardo Otubo wrote: This analysis doesn't make sense to me. On the one hand, you say that the function was crashing if the return from the command wasn't <= 10 bytes long (implying that it sometimes was longer), on the other hand, you say that part of the solution is to change the code to only handle 4 bytes (you forgot about the trailing NULL there, BTW - should have been 3), because you'll never get more than that. Also, your patch doesn't account for the possibility of nids > 1. I don't know anything about the output of lssyscfg other than what I learned from google just now, but it looks like you could end up with multiple lines of output (and this function was certainly written to at least attempt to parse multiple lines, ie multiple ids). Since you error out if the entire string returned from the exec (ret) is > 4 bytes long (again, 3 was what you should have gone for, since you have a 4 byte array and need to reserve one for the NULL), you would fail if there was more than one value returned. You should instead be making sure that *each individual line* is no longer than the limit. Finally, you didn't change the length arg for the 2nd memset that's inside the while loop, thus guaranteeing that you would overwrite 6 bytes of stack every time this function is called. Of course, since virStrToLong_i will stop at the \n ending each line, and not return an error since you're passing an endptr to it, why not just do the conversion directly from the original string instead? That way you wouldn't need to worry about all the memsets, checking for overflows, etc, and you can use the pointer returned from the strtol as the start of the next line, thus eliminating the overly complicated character copy loop. Here's a stab at doing it this way. I haven't even compiled it, but you can give it a try and see if it solves your problem. --- src/phyp/phyp_driver.c | 45 ++++++++++++++++----------------------------- 1 files changed, 16 insertions(+), 29 deletions(-) diff --git a/src/phyp/phyp_driver.c b/src/phyp/phyp_driver.c index ee1e21b..b6e4c5a 100644 --- a/src/phyp/phyp_driver.c +++ b/src/phyp/phyp_driver.c @@ -380,12 +380,10 @@ phypListDomainsGeneric(virConnectPtr conn, int *ids, int nids, int system_type = phyp_driver->system_type; char *managed_system = phyp_driver->managed_system; int exit_status = 0; - int got = 0; - char *char_ptr; - unsigned int i = 0, j = 0; - char id_c[10]; + int got = -1; char *cmd = NULL; char *ret = NULL; + char *line, *next_line; const char *state; virBuffer buf = VIR_BUFFER_INITIALIZER; @@ -394,8 +392,6 @@ phypListDomainsGeneric(virConnectPtr conn, int *ids, int nids, else state = " "; - memset(id_c, 0, 10); - virBufferAddLit(&buf, "lssyscfg -r lpar"); if (system_type == HMC) virBufferVSprintf(&buf, " -m %s", managed_system); @@ -410,37 +406,28 @@ phypListDomainsGeneric(virConnectPtr conn, int *ids, int nids, ret = phypExec(session, cmd, &exit_status, conn); - /* I need to parse the textual return in order to get the ret */ if (exit_status < 0 || ret == NULL) goto err; - else { - while (got < nids) { - if (ret[i] == '\0') - break; - else if (ret[i] == '\n') { - if (virStrToLong_i(id_c, &char_ptr, 10, &ids[got]) == -1) { - VIR_ERROR(_("Cannot parse number from '%s'"), id_c); - goto err; - } - memset(id_c, 0, 10); - j = 0; - got++; - } else { - id_c[j] = ret[i]; - j++; - } - i++; + + /* I need to parse the textual return in order to get the ids */ + line = ret; + got = 0; + while (*line && got < nids) { + if (virStrToLong_i(line, &next_line, 10, &ids[got]) == -1) { + VIR_ERROR(_("Cannot parse number from '%s'"), line); + got = -1; + goto err; } + got++; + line = next_line; + while (*line == '\n') + line++; /* skip \n */ } - VIR_FREE(cmd); - VIR_FREE(ret); - return got; - err: VIR_FREE(cmd); VIR_FREE(ret); - return -1; + return got; } static int -- 1.7.1.1