22a9a3c6f
Denis Vlasenko
2007-05-31
Subject
less: fix very obscure memory corruption bug
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miscutils/less.c+38 -7
| @@ -204,7 +204,27 @@ static void fill_match_lines(unsigned pos); | |
| #define fill_match_lines(pos) ((void)0) | |
| #endif | |
| - | |
| + | /* Devilishly complex routine. |
| + | * |
| + | * Has to deal with EOF and EPIPE on input, |
| + | * with line wrapping, with last line not ending in '\n' |
| + | * (possibly not ending YET!), with backspace and tabs. |
| + | * |
| + | * Variables used: |
| + | * flines[] - array of lines already read. Linewrap may cause |
| + | * one source file line to occupy several flines[n]. |
| + | * flines[max_fline] - last line, possibly incomplete. |
| + | * terminated - 1 if flines[max_fline] is 'terminated' |
| + | * (if there was '\n' [which isn't stored itself, we just remember |
| + | * that it was seen]) |
| + | * max_lineno - last line's number, this one doesn't increment |
| + | * on line wrap, only on "real" new lines. |
| + | * readbuf[0..readeof-1] - small preliminary buffer. |
| + | * readbuf[readpos] - next character to add to current line. |
| + | * linepos - screen line position of next char to be read |
| + | * (takes into account tabs and backspaces) |
| + | * eof_error - < 0 error, == 0 EOF, > 0 not EOF/error |
| + | */ |
| static void read_lines(void) | |
| { | |
| #define readbuf bb_common_bufsiz1 | |
| @@ -225,6 +245,7 @@ static void read_lines(void) | |
| cp += 8; | |
| strcpy(current_line, cp); | |
| p += strlen(current_line); | |
| + | /* linepos is still valid from previous read_lines() */ |
| } else { | |
| linepos = 0; | |
| } | |
| @@ -275,17 +296,27 @@ static void read_lines(void) | |
| if (c == '\x8' && linepos && p[-1] != '\t') { | |
| readpos++; /* eat it */ | |
| linepos--; | |
| + | /* was buggy (p could end up <= current_line)... */ |
| *--p = '\0'; | |
| continue; | |
| } | |
| - | if (c == '\t') |
| - | linepos += (linepos^7) & 7; |
| - | linepos++; |
| - | if (linepos >= w) |
| - | break; |
| + | { |
| + | size_t new_linepos = linepos + 1; |
| + | if (c == '\t') { |
| + | new_linepos += 7; |
| + | new_linepos &= (~7); |
| + | } |
| + | if (new_linepos >= w) |
| + | break; |
| + | linepos = new_linepos; |
| + | } |
| /* ok, we will eat this char */ | |
| readpos++; | |
| - | if (c == '\n') { terminated = 1; break; } |
| + | if (c == '\n') { |
| + | terminated = 1; |
| + | linepos = 0; |
| + | break; |
| + | } |
| /* NUL is substituted by '\n'! */ | |
| if (c == '\0') c = '\n'; | |
| *p++ = c; | |