tree d069b6ec58e6ab070fea9bf481c4133d05cdb9c5
parent 2a68be109c4aac64b4cc9143d0aaa1bb8d77c5d4
author Phil Sutter <phil@nwl.cc> 1537184313 +0200
committer Pablo Neira Ayuso <pablo@netfilter.org> 1537226239 +0200

libxt_string: Fix array out of bounds check

Commit 56d7ab42f3782 ("libxt_string: Avoid potential array out of bounds
access") tried to fix parse_hex_string() for overlong strings but the
change still allowed for 'sindex' to become XT_STRING_MAX_PATTERN_SIZE
which leads to access of first byte after info->pattern. This is not
really a problem because it merely overwrites info->patlen before
calling xtables_error() later, but covscan still detects it so it's
still worth fixing.

The crucial bit here is that 'sindex' has to be incremented at end of
the last iteration since its value is used for info->patlen. Hence just
move the overflow check to the beginning of the loop.

Fixes: 56d7ab42f3782 ("libxt_string: Avoid potential array out of bounds access")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>