X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=blobdiff_plain;f=src%2Fjournal%2Fmmap-cache.c;h=ab21cdc28873e36ac88465336252caa44cef4a4d;hb=93a1e66efd4b0f4cda29c467d20d0f7510c0b3a8;hp=117dc2f3a5b81c27cf5b8838de001e3cceda3340;hpb=bf807d4dbf27c783db8dfd7f4eca321ae4be5b00;p=elogind.git

diff --git a/src/journal/mmap-cache.c b/src/journal/mmap-cache.c
index 117dc2f3a..ab21cdc28 100644
--- a/src/journal/mmap-cache.c
+++ b/src/journal/mmap-cache.c
@@ -29,6 +29,7 @@
 #include "log.h"
 #include "util.h"
 #include "macro.h"
+#include "sigbus.h"
 #include "mmap-cache.h"
 
 typedef struct Window Window;
@@ -38,6 +39,7 @@ typedef struct FileDescriptor FileDescriptor;
 struct Window {
         MMapCache *cache;
 
+        bool invalidated;
         bool keep_always;
         bool in_unused;
 
@@ -65,6 +67,7 @@ struct Context {
 struct FileDescriptor {
         MMapCache *cache;
         int fd;
+        bool sigbus;
         LIST_HEAD(Window, windows);
 };
 
@@ -76,14 +79,20 @@ struct MMapCache {
 
 
         Hashmap *fds;
-        Hashmap *contexts;
+        Context *contexts[MMAP_CACHE_MAX_CONTEXTS];
 
         LIST_HEAD(Window, unused);
         Window *last_unused;
 };
 
 #define WINDOWS_MIN 64
-#define WINDOW_SIZE (8ULL*1024ULL*1024ULL)
+
+#ifdef ENABLE_DEBUG_MMAP_CACHE
+/* Tiny windows increase mmap activity and the chance of exposing unsafe use. */
+# define WINDOW_SIZE (page_size())
+#else
+# define WINDOW_SIZE (8ULL*1024ULL*1024ULL)
+#endif
 
 MMapCache* mmap_cache_new(void) {
         MMapCache *m;
@@ -128,6 +137,21 @@ static void window_unlink(Window *w) {
         }
 }
 
+static void window_invalidate(Window *w) {
+        assert(w);
+
+        if (w->invalidated)
+                return;
+
+        /* Replace the window with anonymous pages. This is useful
+         * when we hit a SIGBUS and want to make sure the file cannot
+         * trigger any further SIGBUS, possibly overrunning the sigbus
+         * queue. */
+
+        assert_se(mmap(w->ptr, w->size, w->prot, MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0) == w->ptr);
+        w->invalidated = true;
+}
+
 static void window_free(Window *w) {
         assert(w);
 
@@ -187,11 +211,17 @@ static void context_detach_window(Context *c) {
 
         if (!w->contexts && !w->keep_always) {
                 /* Not used anymore? */
+#ifdef ENABLE_DEBUG_MMAP_CACHE
+                /* Unmap unused windows immediately to expose use-after-unmap
+                 * by SIGSEGV. */
+                window_free(w);
+#else
                 LIST_PREPEND(unused, c->cache->unused, w);
                 if (!c->cache->last_unused)
                         c->cache->last_unused = w;
 
                 w->in_unused = true;
+#endif
         }
 }
 
@@ -219,18 +249,13 @@ static void context_attach_window(Context *c, Window *w) {
 
 static Context *context_add(MMapCache *m, unsigned id) {
         Context *c;
-        int r;
 
         assert(m);
 
-        c = hashmap_get(m->contexts, UINT_TO_PTR(id + 1));
+        c = m->contexts[id];
         if (c)
                 return c;
 
-        r = hashmap_ensure_allocated(&m->contexts, trivial_hash_func, trivial_compare_func);
-        if (r < 0)
-                return NULL;
-
         c = new0(Context, 1);
         if (!c)
                 return NULL;
@@ -238,11 +263,8 @@ static Context *context_add(MMapCache *m, unsigned id) {
         c->cache = m;
         c->id = id;
 
-        r = hashmap_put(m->contexts, UINT_TO_PTR(id + 1), c);
-        if (r < 0) {
-                free(c);
-                return NULL;
-        }
+        assert(!m->contexts[id]);
+        m->contexts[id] = c;
 
         return c;
 }
@@ -252,8 +274,10 @@ static void context_free(Context *c) {
 
         context_detach_window(c);
 
-        if (c->cache)
-                assert_se(hashmap_remove(c->cache->contexts, UINT_TO_PTR(c->id + 1)));
+        if (c->cache) {
+                assert(c->cache->contexts[c->id] == c);
+                c->cache->contexts[c->id] = NULL;
+        }
 
         free(c);
 }
@@ -281,7 +305,7 @@ static FileDescriptor* fd_add(MMapCache *m, int fd) {
         if (f)
                 return f;
 
-        r = hashmap_ensure_allocated(&m->fds, trivial_hash_func, trivial_compare_func);
+        r = hashmap_ensure_allocated(&m->fds, NULL);
         if (r < 0)
                 return NULL;
 
@@ -302,15 +326,14 @@ static FileDescriptor* fd_add(MMapCache *m, int fd) {
 }
 
 static void mmap_cache_free(MMapCache *m) {
-        Context *c;
         FileDescriptor *f;
+        int i;
 
         assert(m);
 
-        while ((c = hashmap_first(m->contexts)))
-                context_free(c);
-
-        hashmap_free(m->contexts);
+        for (i = 0; i < MMAP_CACHE_MAX_CONTEXTS; i++)
+                if (m->contexts[i])
+                        context_free(m->contexts[i]);
 
         while ((f = hashmap_first(m->fds)))
                 fd_free(f);
@@ -362,7 +385,7 @@ static int try_context(
         assert(size > 0);
         assert(ret);
 
-        c = hashmap_get(m->contexts, UINT_TO_PTR(context+1));
+        c = m->contexts[context];
         if (!c)
                 return 0;
 
@@ -378,7 +401,10 @@ static int try_context(
                 return 0;
         }
 
-        c->window->keep_always = c->window->keep_always || keep_always;
+        if (c->window->fd->sigbus)
+                return -EIO;
+
+        c->window->keep_always |= keep_always;
 
         *ret = (uint8_t*) c->window->ptr + (offset - c->window->offset);
         return 1;
@@ -402,7 +428,6 @@ static int find_mmap(
         assert(m->n_ref > 0);
         assert(fd >= 0);
         assert(size > 0);
-        assert(ret);
 
         f = hashmap_get(m->fds, INT_TO_PTR(fd + 1));
         if (!f)
@@ -410,6 +435,9 @@ static int find_mmap(
 
         assert(f->fd == fd);
 
+        if (f->sigbus)
+                return -EIO;
+
         LIST_FOREACH(by_fd, w, f->windows)
                 if (window_matches(w, fd, prot, offset, size))
                         break;
@@ -422,7 +450,7 @@ static int find_mmap(
                 return -ENOMEM;
 
         context_attach_window(c, w);
-        w->keep_always = w->keep_always || keep_always;
+        w->keep_always += keep_always;
 
         *ret = (uint8_t*) w->ptr + (offset - w->offset);
         return 1;
@@ -497,15 +525,15 @@ static int add_mmap(
 
         c = context_add(m, context);
         if (!c)
-                return -ENOMEM;
+                goto outofmem;
 
         f = fd_add(m, fd);
         if (!f)
-                return -ENOMEM;
+                goto outofmem;
 
         w = window_add(m);
         if (!w)
-                return -ENOMEM;
+                goto outofmem;
 
         w->keep_always = keep_always;
         w->ptr = d;
@@ -522,6 +550,10 @@ static int add_mmap(
 
         *ret = (uint8_t*) w->ptr + (offset - w->offset);
         return 1;
+
+outofmem:
+        munmap(d, wsize);
+        return -ENOMEM;
 }
 
 int mmap_cache_get(
@@ -542,6 +574,7 @@ int mmap_cache_get(
         assert(fd >= 0);
         assert(size > 0);
         assert(ret);
+        assert(context < MMAP_CACHE_MAX_CONTEXTS);
 
         /* Check whether the current context is the right one already */
         r = try_context(m, fd, prot, context, keep_always, offset, size, ret);
@@ -563,39 +596,111 @@ int mmap_cache_get(
         return add_mmap(m, fd, prot, context, keep_always, offset, size, st, ret);
 }
 
-void mmap_cache_close_fd(MMapCache *m, int fd) {
-        FileDescriptor *f;
-
+unsigned mmap_cache_get_hit(MMapCache *m) {
         assert(m);
-        assert(fd >= 0);
 
-        f = hashmap_get(m->fds, INT_TO_PTR(fd + 1));
-        if (!f)
-                return;
+        return m->n_hit;
+}
 
-        fd_free(f);
+unsigned mmap_cache_get_missed(MMapCache *m) {
+        assert(m);
+
+        return m->n_missed;
 }
 
-void mmap_cache_close_context(MMapCache *m, unsigned context) {
-        Context *c;
+static void mmap_cache_process_sigbus(MMapCache *m) {
+        bool found = false;
+        FileDescriptor *f;
+        Iterator i;
+        int r;
 
         assert(m);
 
-        c = hashmap_get(m->contexts, UINT_TO_PTR(context + 1));
-        if (!c)
+        /* Iterate through all triggered pages and mark their files as
+         * invalidated */
+        for (;;) {
+                bool ours;
+                void *addr;
+
+                r = sigbus_pop(&addr);
+                if (_likely_(r == 0))
+                        break;
+                if (r < 0) {
+                        log_error_errno(r, "SIGBUS handling failed: %m");
+                        abort();
+                }
+
+                ours = false;
+                HASHMAP_FOREACH(f, m->fds, i) {
+                        Window *w;
+
+                        LIST_FOREACH(by_fd, w, f->windows) {
+                                if ((uint8_t*) addr >= (uint8_t*) w->ptr &&
+                                    (uint8_t*) addr < (uint8_t*) w->ptr + w->size) {
+                                        found = ours = f->sigbus = true;
+                                        break;
+                                }
+                        }
+
+                        if (ours)
+                                break;
+                }
+
+                /* Didn't find a matching window, give up */
+                if (!ours) {
+                        log_error("Unknown SIGBUS page, aborting.");
+                        abort();
+                }
+        }
+
+        /* The list of triggered pages is now empty. Now, let's remap
+         * all windows of the triggered file to anonymous maps, so
+         * that no page of the file in question is triggered again, so
+         * that we can be sure not to hit the queue size limit. */
+        if (_likely_(!found))
                 return;
 
-        context_free(c);
+        HASHMAP_FOREACH(f, m->fds, i) {
+                Window *w;
+
+                if (!f->sigbus)
+                        continue;
+
+                LIST_FOREACH(by_fd, w, f->windows)
+                        window_invalidate(w);
+        }
 }
 
-unsigned mmap_cache_get_hit(MMapCache *m) {
+bool mmap_cache_got_sigbus(MMapCache *m, int fd) {
+        FileDescriptor *f;
+
         assert(m);
+        assert(fd >= 0);
 
-        return m->n_hit;
+        mmap_cache_process_sigbus(m);
+
+        f = hashmap_get(m->fds, INT_TO_PTR(fd + 1));
+        if (!f)
+                return false;
+
+        return f->sigbus;
 }
 
-unsigned mmap_cache_get_missed(MMapCache *m) {
+void mmap_cache_close_fd(MMapCache *m, int fd) {
+        FileDescriptor *f;
+
         assert(m);
+        assert(fd >= 0);
 
-        return m->n_missed;
+        /* Make sure that any queued SIGBUS are first dispatched, so
+         * that we don't end up with a SIGBUS entry we cannot relate
+         * to any existing memory map */
+
+        mmap_cache_process_sigbus(m);
+
+        f = hashmap_get(m->fds, INT_TO_PTR(fd + 1));
+        if (!f)
+                return;
+
+        fd_free(f);
 }