top: provide some protection against forking anomalies
This commit will eliminate a very nasty bug associated with top's forest view mode. It addresses a potential SIGSEGV/SIGABRT that was only encountered when another program (erroneously?) creates a lengthy forking loop. If the growing list of nested children is sufficiently fast such that proc_t start_time is duplicated between children then the sort upon which top relies might not produce the expected order. That, in turn, could cause the forest_adds function to initially miss some child. But that missed child would be caught by forest_create and eventually would cause our array boundary overrun. Such overrun occurs when some child of that originally *missed* child is found and a duplicate add attempted. In correcting this bug we'll also use this opportunity to prohibit a borrowed proc_t padding byte (char) from going negative. If the nesting level exceeded 127, the effect was an "unnesting" with the snprintf width then viewed as flag+width also yielding left justification. Henceforth, we'll limit nesting to 100 with subsequent children shown as " + ", not the usual " `- " prefix. References(s): https://bugzilla.redhat.com/show_bug.cgi?id=1153642 http://www.freelists.org/post/procps/Bug-in-the-forrest-view,6 Signed-off-by: Jim Warner <james.warner@comcast.net>
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top/top.c
15
top/top.c
@ -4895,22 +4895,24 @@ static void keys_xtra (int ch) {
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* ( plus, maintain alphabetical order with carefully chosen )
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* ( function names: forest_a, forest_b, forest_c & forest_d )
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* ( each with exactly one letter more than its predecessor! ) */
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static proc_t **Seed_ppt; // temporary window ppt ptr
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static proc_t **Tree_ppt; // resized by forest_create
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static int Tree_idx; // frame_make initializes
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static proc_t **Seed_ppt; // temporary win ppt pointer
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static proc_t **Tree_ppt; // forest_create will resize
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static int Tree_idx; // frame_make resets to zero
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/*
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* This little recursive guy is the real forest view workhorse.
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* He fills in the Tree_ppt array and also sets the child indent
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* level which is stored in an unused proc_t padding byte. */
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static void forest_adds (const int self, const int level) {
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static void forest_adds (const int self, int level) {
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int i;
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if (level > 100) level = 101; // our arbitrary nests limit
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Tree_ppt[Tree_idx] = Seed_ppt[self]; // add this as root or child
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Tree_ppt[Tree_idx++]->pad_3 = level; // borrow 1 byte, 127 levels
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for (i = self + 1; i < Frame_maxtask; i++) {
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if (Seed_ppt[self]->tid == Seed_ppt[i]->tgid
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if ((Seed_ppt[self]->tid == Seed_ppt[i]->tgid
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|| (Seed_ppt[self]->tid == Seed_ppt[i]->ppid && Seed_ppt[i]->tid == Seed_ppt[i]->tgid))
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&& Tree_idx < Frame_maxtask) // shouldn't happen, but has
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forest_adds(i, level + 1); // got one child any others?
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}
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} // end: forest_adds
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@ -4963,7 +4965,8 @@ static inline const char *forest_display (const WIN_t *q, const proc_t *p) {
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const char *which = (CHKw(q, Show_CMDLIN)) ? *p->cmdline : p->cmd;
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if (!CHKw(q, Show_FOREST) || 1 == p->pad_3) return which;
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snprintf(buf, sizeof(buf), "%*s%s", 4 * (p->pad_3 - 1), " `- ", which);
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if (p->pad_3 > 100) snprintf(buf, sizeof(buf), "%400s%s", " + ", which);
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else snprintf(buf, sizeof(buf), "%*s%s", 4 * (p->pad_3 - 1), " `- ", which);
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return buf;
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} // end: forest_display
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@ -780,7 +780,7 @@ typedef struct WIN_t {
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//atic void keys_window (int ch);
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//atic void keys_xtra (int ch);
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/*------ Forest View support -------------------------------------------*/
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//atic void forest_adds (const int self, const int level);
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//atic void forest_adds (const int self, int level);
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//atic int forest_based (const proc_t **x, const proc_t **y);
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//atic void forest_create (WIN_t *q);
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//atic inline const char *forest_display (const WIN_t *q, const proc_t *p);
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