On Fri, Jul 28, 2017 at 01:19:39PM +0200, Theo Buehler wrote:
> On Thu, Jul 27, 2017 at 10:31:51AM +0100, Larry Hynes wrote:
> > Hi
> >
> > $ env | grep LESS
> > LESSHISTFILE=-
> > LESS="-i -M -R -g -c"
> > LESSCHARSET=utf-8
> >
> > $ unset LESS
> > $ unset LESSCHARSET
> > $ unset LESSHISTFILE
> >
> > $ LESS="-g"
> > $ echo 'foo\nbar\nfoo\nbar\nfoo\nbar' | less
> >
> > While in less, '/' to search, then '^N', or '!', to search for lines
> > which do NOT match the pattern, entering foo<CR> results in a seg
> > fault.
> >
> > This is on amd64.
>
> Thanks for the report. Of course you want 'export LESS="-g"' here,
> otherwise less(1) won't use the -g flag which is crucial for this crash.
>
> I don't have a fix, but maybe this helps a bit:
>
> From the command line, without environment variable magic and no
> interactive component you can reproduce as follows:
>
> $ echo 'foo\nbar\nfoo\n' > crash
> $ less -g -p '!foo' crash
>
> It's apparently a use-after-free that happens in search_range():
>
> Program terminated with signal SIGSEGV, Segmentation fault.
> #0 0x000009d426e1b35b in create_hilites (linepos=4, start_index=-370944992,
> end_index=-370944989, chpos=0x9d6c5994c80)
> at /usr/src/usr.bin/less/less/../search.c:445
> 445 hl->hl_startpos = linepos + chpos[start_index];
> (gdb) bt
> #0 0x000009d426e1b35b in create_hilites (linepos=4, start_index=-370944992,
> end_index=-370944989, chpos=0x9d6c5994c80)
> at /usr/src/usr.bin/less/less/../search.c:445
> #1 0x000009d426e1b24c in hilite_line (linepos=4, line=0x9d65872bf70 "bar",
> line_len=3, chpos=0x9d6c5994c80,
> sp=0x9d642569390 '\337' <repeats 15 times>, <incomplete sequence \337>,
> ep=0x9d642569393 '\337' <repeats 12 times>, <incomplete sequence \337>)
> at /usr/src/usr.bin/less/less/../search.c:494
> #2 0x000009d426e1aa99 in search_range (pos=8, endpos=-1, search_type=257,
> matches=0, maxlines=-1, plinepos=0x7f7ffffe9ff0,
> pendpos=0x0) at /usr/src/usr.bin/less/less/../search.c:804
> #3 0x000009d426e1a258 in search (search_type=257, pattern=0x9d42702ca40
> <cmdbuf> "foo", n=1)
> at /usr/src/usr.bin/less/less/../search.c:925
> #4 0x000009d426e0a182 in multi_search (pattern=0x9d42702ca40 <cmdbuf> "foo",
> n=1) at /usr/src/usr.bin/less/less/../command.c:815
> #5 0x000009d426e0a779 in exec_mca () at
> /usr/src/usr.bin/less/less/../command.c:189
> #6 0x000009d426e09d03 in mca_char (c=10) at
> /usr/src/usr.bin/less/less/../command.c:532
> #7 0x000009d426e08865 in commands () at
> /usr/src/usr.bin/less/less/../command.c:971
> #8 0x000009d426e010f2 in main (argc=-1, argv=0x7f7ffffea200) at
> /usr/src/usr.bin/less/less/../main.c:274
>
I took a closer look earlier today. As I see it, {start,end}_index does
not get updated inside match_pattern() since we're looking for inverted
matches, i.e. when regexec() indicates no match we actually got a match.
Instead, the indices could be set to NULL up front and the corresponding
NULL-check moved into the loop since match_pattern() is called
repeatedly. Tested with and without `-g` for both normal and inverted
search.
Index: pattern.c
===================================================================
RCS file: /cvs/src/usr.bin/less/pattern.c,v
retrieving revision 1.9
diff -u -p -r1.9 pattern.c
--- pattern.c 21 Nov 2015 13:29:12 -0000 1.9
+++ pattern.c 28 Jul 2017 11:31:34 -0000
@@ -122,6 +122,8 @@ match_pattern(void *pattern, char *tpatt
rm.rm_so = 0;
rm.rm_eo = line_len;
#endif
+ *sp = NULL;
+ *ep = NULL;
matched = !regexec(spattern, line, 1, &rm, flags);
if (matched) {
*sp = line + rm.rm_so;
Index: search.c
===================================================================
RCS file: /cvs/src/usr.bin/less/search.c,v
retrieving revision 1.18
diff -u -p -r1.18 search.c
--- search.c 17 Sep 2016 15:06:41 -0000 1.18
+++ search.c 28 Jul 2017 11:31:34 -0000
@@ -477,8 +477,6 @@ hilite_line(off_t linepos, char *line, i
char *searchp;
char *line_end = line + line_len;
- if (sp == NULL || ep == NULL)
- return;
/*
* sp and ep delimit the first match in the line.
* Mark the corresponding file positions, then
@@ -491,6 +489,9 @@ hilite_line(off_t linepos, char *line, i
*/
searchp = line;
do {
+ if (sp == NULL || ep == NULL)
+ return;
+
create_hilites(linepos, (intptr_t)sp - (intptr_t)line,
(intptr_t)ep - (intptr_t)line, chpos);
/*
