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libpkgconf: dependency: fix out of boundary write 

It is possible to trigger an out of boundary write in function
pkgconf_dependency_parse_str if a dependency line contains a very
long comparator. The comparator is stored in a temporary buffer which
has a size of PKGCONF_ITEM_SIZE.

The line which is parsed can be up to PKGCONF_BUFSIZE characters long,
which is larger than PKGCONF_ITEM_SIZE (although it depends on PATH_MAX).

Having a comparator which is longer than PKGCONF_ITEM_SIZE therefore
leads to an out of boundary write. Although it is undefined behaviour,
this can lead to an overridden compare variable, which in turn can lead
to an invalid instruction pointer, i.e. most likely a crash or code
execution (very unlikely).

Proof of concept:

$ echo "Requires: x " > poc.pc
$ dd if=/dev/zero bs=1 count=65535 | tr '\0' '<' >> poc.pc
$ pkgconf poc.pc

Eiter compile pkgconf with address sanitizer or run pkgconf multiple
times, eventually it might crash (assuming that ASLR is in place).

In order to fix this, I decided to use an end pointer to avoid OOB write.
Alternative would be to increase the buffer size, but I try to avoid that
since this would be additional ~60 KB stack space for a very unlikely
situation.
master
Tobias Stoeckmann 2020-05-26 21:42:13 +02:00 committed by Ariadne Conill
parent c6b93941a0
commit fb9acedcad
1 changed files with 4 additions and 2 deletions
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6
libpkgconf/dependency.c
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@ -237,6 +237,7 @@ pkgconf_dependency_parse_str(const pkgconf_client_t *client, pkgconf_list_t *dep
char *vstart = NULL; char *vstart = NULL;
char *package = NULL, *version = NULL; char *package = NULL, *version = NULL;
char *cnameptr = cmpname; char *cnameptr = cmpname;
char *cnameend = cmpname + PKGCONF_ITEM_SIZE - 1;
memset(cmpname, '\0', sizeof cmpname); memset(cmpname, '\0', sizeof cmpname);
@ -304,7 +305,8 @@ pkgconf_dependency_parse_str(const pkgconf_client_t *client, pkgconf_list_t *dep
if (PKGCONF_IS_OPERATOR_CHAR(*ptr)) if (PKGCONF_IS_OPERATOR_CHAR(*ptr))
{ {
state = INSIDE_OPERATOR; state = INSIDE_OPERATOR;
*cnameptr++ = *ptr; if (cnameptr < cnameend)
*cnameptr++ = *ptr;
} }
break; break;
@ -315,7 +317,7 @@ pkgconf_dependency_parse_str(const pkgconf_client_t *client, pkgconf_list_t *dep
state = AFTER_OPERATOR; state = AFTER_OPERATOR;
compare = pkgconf_pkg_comparator_lookup_by_name(cmpname); compare = pkgconf_pkg_comparator_lookup_by_name(cmpname);
} }
else else if (cnameptr < cnameend)
*cnameptr++ = *ptr; *cnameptr++ = *ptr;
break; break;