[Qemu-devel] [PATCH] rev3: support colon in filenames

[Ram Pai]

Problem: It is impossible to feed filenames with the character colon because
qemu interprets such names as a protocol. For example filename scsi:0, is
interpreted as a protocol by name "scsi".

This patch allows user to escape colon characters. For example the above
filename can now be expressed either as 'scsi\:0' or as file:scsi:0

anything following the "file:" tag is interpreted verbatim. However if "file:"
tag is omitted then any colon characters in the string must be escaped using
backslash.

Here are couple of examples:

scsi\:0\:abc is a local file scsi:0:abc
http\://myweb is a local file by name http://myweb
file:scsi:0:abc is a local file scsi:0:abc
file:http://myweb is a local file by name http://myweb

fat:c:\path\to\dir\:floppy\:  is a fat file by name \path\to\dir:floppy:
NOTE:The above example cannot be expressed using the "file:" protocol.


Changelog w.r.t to iteration 0:
   1) removes flexibility added to nbd semantics  eg -- nbd:\::9999
   2) introduce the file: protocol to indicate local file

Changelog w.r.t to iteration 1:
   1) generically handles 'file:' protocol in find_protocol
   2) centralizes 'filename' pruning before the call to open().
   3) fixes buffer overflow seen in fill_token()
   4) adheres to coding style
   5) patch against upstream qemu tree

Changelog w.r.t to iteration 2:
   1) really really fixes buffer overflow seen in fill_token()
   2) the centralized 'filename' pruning had a side effect with
        qcow2 files and other files. Fixed it. _open() is back.

Signed-off-by: Ram Pai <address@hidden>

 block.c           |   10 +----
 block/raw-posix.c |   15 ++++----
 block/vvfat.c     |  100 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 cutils.c          |   40 +++++++++++++++++++++
 qemu-common.h     |    2 +
 5 files changed, 148 insertions(+), 19 deletions(-)

diff --git a/block.c b/block.c
index aca5a6d..7ad4dd9 100644
--- a/block.c
+++ b/block.c
@@ -225,7 +225,6 @@ static BlockDriver *find_protocol(const char *filename)
 {
     BlockDriver *drv1;
     char protocol[128];
-    int len;
     const char *p;
 
 #ifdef _WIN32
@@ -233,14 +232,9 @@ static BlockDriver *find_protocol(const char *filename)
         is_windows_drive_prefix(filename))
         return bdrv_find_format("raw");
 #endif
-    p = strchr(filename, ':');
-    if (!p)
+    p = prune_strcpy(protocol, 128, filename, ':');
+    if (*p != ':')
         return bdrv_find_format("raw");
-    len = p - filename;
-    if (len > sizeof(protocol) - 1)
-        len = sizeof(protocol) - 1;
-    memcpy(protocol, filename, len);
-    protocol[len] = '\0';
     for(drv1 = first_drv; drv1 != NULL; drv1 = drv1->next) {
         if (drv1->protocol_name &&
             !strcmp(drv1->protocol_name, protocol))
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 41bfa37..8a0c0df 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -151,7 +151,7 @@ static int raw_open_common(BlockDriverState *bs, const char 
*filename,
         s->open_flags |= O_DSYNC;
 
     s->fd = -1;
-    fd = open(filename, s->open_flags, 0644);
+    fd = _open(filename, s->open_flags, 0644);
     if (fd < 0) {
         ret = -errno;
         if (ret == -EROFS)
@@ -844,7 +844,7 @@ static int raw_create(const char *filename, 
QEMUOptionParameter *options)
         options++;
     }
 
-    fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
+    fd = _open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
               0644);
     if (fd < 0)
         return -EIO;
@@ -889,6 +889,7 @@ static BlockDriver bdrv_raw = {
     .bdrv_getlength = raw_getlength,
 
     .create_options = raw_create_options,
+    .protocol_name = "file",
 };
 
 /***********************************************/
@@ -985,7 +986,7 @@ static int hdev_open(BlockDriverState *bs, const char 
*filename, int flags)
         if ( bsdPath[ 0 ] != '\0' ) {
             strcat(bsdPath,"s0");
             /* some CDs don't have a partition 0 */
-            fd = open(bsdPath, O_RDONLY | O_BINARY | O_LARGEFILE);
+            fd = _open(bsdPath, O_RDONLY | O_BINARY | O_LARGEFILE);
             if (fd < 0) {
                 bsdPath[strlen(bsdPath)-1] = '1';
             } else {
@@ -1037,7 +1038,7 @@ static int fd_open(BlockDriverState *bs)
 #endif
             return -EIO;
         }
-        s->fd = open(bs->filename, s->open_flags & ~O_NONBLOCK);
+        s->fd = _open(bs->filename, s->open_flags & ~O_NONBLOCK);
         if (s->fd < 0) {
             s->fd_error_time = qemu_get_clock(rt_clock);
             s->fd_got_error = 1;
@@ -1133,7 +1134,7 @@ static int hdev_create(const char *filename, 
QEMUOptionParameter *options)
         options++;
     }
 
-    fd = open(filename, O_WRONLY | O_BINARY);
+    fd = _open(filename, O_WRONLY | O_BINARY);
     if (fd < 0)
         return -EIO;
 
@@ -1239,7 +1240,7 @@ static int floppy_eject(BlockDriverState *bs, int 
eject_flag)
         close(s->fd);
         s->fd = -1;
     }
-    fd = open(bs->filename, s->open_flags | O_NONBLOCK);
+    fd = _open(bs->filename, s->open_flags | O_NONBLOCK);
     if (fd >= 0) {
         if (ioctl(fd, FDEJECT, 0) < 0)
             perror("FDEJECT");
@@ -1399,7 +1400,7 @@ static int cdrom_reopen(BlockDriverState *bs)
      */
     if (s->fd >= 0)
         close(s->fd);
-    fd = open(bs->filename, s->open_flags, 0644);
+    fd = _open(bs->filename, s->open_flags, 0644);
     if (fd < 0) {
         s->fd = -1;
         return -EIO;
diff --git a/block/vvfat.c b/block/vvfat.c
index 1e37b9f..4729165 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -76,6 +76,97 @@ typedef struct array_t {
     unsigned int size,next,item_size;
 } array_t;
 
+/*
+ * prunes out all escape characters as per the following rule
+ * '\\' -> '\'
+ * '\:' -> ':'
+ * '\,' -> ','
+ * '\x' -> '\x'
+ * return a new pruned string.
+ * NOTE: remember to free that string.
+ */
+static char *escape_strdup(const char *str)
+{
+#define NORMAL  0
+#define ESCAPED 1
+    int len = strlen(str);
+    char *s = qemu_malloc(len+1);
+    char *q = s;
+    const char *p=str;
+    int state=NORMAL;
+
+    while (p < str+len) {
+        switch (state) {
+        case NORMAL:
+            switch (*p) {
+            case '\\' : state=ESCAPED; p++ ; break;
+            default: *q++=*p++; break;
+            }
+           break;
+        case ESCAPED:
+            switch (*p) {
+            case '\\' :
+            case ',' :
+            case ':':
+                     break;
+
+            default: *q++='\\';break;
+            }
+            state = NORMAL;
+            *q++=*p++;
+           break;
+        }
+   }
+   *q = '\0';
+   return s;
+}
+
+/*
+ * return the index of the rightmost delimitor in the string 'str'
+ */
+static int find_rdelim(const char *str, const char delimitor)
+{
+#define NOT_FOUND 1
+#define MAY_HAVE_FOUND 2
+#define MAY_NOT_HAVE_FOUND 3
+    const char *f = str + strlen(str) -1;
+    char state = NOT_FOUND;
+    const char *loc = f;
+
+    while (f >= str) {
+        char c = *f--;
+        switch (state) {
+        case NOT_FOUND:
+            if (c == delimitor) {
+                state=MAY_HAVE_FOUND;
+                loc=f+1;
+            }
+            break;
+        case MAY_HAVE_FOUND:
+            if (c == '\\') {
+                 state=MAY_NOT_HAVE_FOUND;
+            } else {
+                 goto out;
+            }
+            break;
+        case MAY_NOT_HAVE_FOUND:
+            if (c == '\\') {
+                state=MAY_HAVE_FOUND;
+            } else if ( c == delimitor ) {
+                state=MAY_HAVE_FOUND;
+                loc=f+1;
+            } else {
+                state=NOT_FOUND;
+            }
+            break;
+        }
+    }
+    loc=f;
+out:
+    return (loc-str);
+}
+
+
 static inline void array_init(array_t* array,unsigned int item_size)
 {
     array->pointer = NULL;
@@ -882,7 +973,7 @@ static int init_directories(BDRVVVFATState* s,
     mapping->dir_index = 0;
     mapping->info.dir.parent_mapping_index = -1;
     mapping->first_mapping_index = -1;
-    mapping->path = strdup(dirname);
+    mapping->path = escape_strdup(dirname);
     i = strlen(mapping->path);
     if (i > 0 && mapping->path[i - 1] == '/')
        mapping->path[i - 1] = '\0';
@@ -1055,7 +1146,7 @@ DLOG(if (stderr == NULL) {
        bs->read_only = 0;
     }
 
-    i = strrchr(dirname, ':') - dirname;
+    i = find_rdelim(dirname, ':'); /* find the rightmost unescaped colon */
     assert(i >= 3);
     if (dirname[i-2] == ':' && qemu_isalpha(dirname[i-1]))
        /* workaround for DOS drive names */
@@ -1081,6 +1172,7 @@ DLOG(if (stderr == NULL) {
     return 0;
 }
 
+
 static inline void vvfat_close_current_file(BDRVVVFATState *s)
 {
     if(s->current_mapping) {
@@ -1162,7 +1254,7 @@ static int open_file(BDRVVVFATState* s,mapping_t* mapping)
     if(!s->current_mapping ||
            strcmp(s->current_mapping->path,mapping->path)) {
        /* open file */
-       int fd = open(mapping->path, O_RDONLY | O_BINARY | O_LARGEFILE);
+       int fd = _open(mapping->path, O_RDONLY | O_BINARY | O_LARGEFILE);
        if(fd<0)
            return -1;
        vvfat_close_current_file(s);
@@ -2222,7 +2314,7 @@ static int commit_one_file(BDRVVVFATState* s,
     for (i = s->cluster_size; i < offset; i += s->cluster_size)
        c = modified_fat_get(s, c);
 
-    fd = open(mapping->path, O_RDWR | O_CREAT | O_BINARY, 0666);
+    fd = _open(mapping->path, O_RDWR | O_CREAT | O_BINARY, 0666);
     if (fd < 0) {
        fprintf(stderr, "Could not open %s... (%s, %d)\n", mapping->path,
                strerror(errno), errno);
diff --git a/cutils.c b/cutils.c
index 6ea0c49..05f570b 100644
--- a/cutils.c
+++ b/cutils.c
@@ -24,6 +24,32 @@
 #include "qemu-common.h"
 #include "host-utils.h"
 
+/*
+ * copy contents of 'str' into buf until the first unescaped
+ * character 'c'. Escape character '\' is pruned off.
+ * Return pointer to the delimiting character
+ */
+const char *prune_strcpy(char *buf, int len, const char *str, const char c)
+{
+    const char *p=str;
+    char *q=buf;
+
+    len = strnlen(str, len-1);
+    while (p < str+len) {
+        if (*p == c)
+            break;
+        if (*p == '\\') {
+            p++;
+            if (*p == '\0')
+                break;
+        }
+        *q++ = *p++;
+    }
+    *q='\0';
+    return p;
+}
+
+
 void pstrcpy(char *buf, int buf_size, const char *str)
 {
     int c;
@@ -184,3 +210,17 @@ void qemu_iovec_from_buffer(QEMUIOVector *qiov, const void 
*buf, size_t count)
         count -= copy;
     }
 }
+
+int _open(const char *filename, int flags, ...)
+{
+    char myfile[PATH_MAX];
+    const char *f;
+    va_list ap;
+    va_start(ap, flags);
+
+    if (!strstart(filename, "file:", &f)) {
+        prune_strcpy(myfile, PATH_MAX, filename, '\0');
+        return  open(myfile, flags, ap);
+    }
+    return  open(f, flags, ap);
+}
diff --git a/qemu-common.h b/qemu-common.h
index 2dcb224..41da8b0 100644
--- a/qemu-common.h
+++ b/qemu-common.h
@@ -104,12 +104,14 @@ void qemu_get_timedate(struct tm *tm, int offset);
 int qemu_timedate_diff(struct tm *tm);
 
 /* cutils.c */
+const char *prune_strcpy(char *buf, int buf_size, const char *str, const char);
 void pstrcpy(char *buf, int buf_size, const char *str);
 char *pstrcat(char *buf, int buf_size, const char *s);
 int strstart(const char *str, const char *val, const char **ptr);
 int stristart(const char *str, const char *val, const char **ptr);
 time_t mktimegm(struct tm *tm);
 int qemu_fls(int i);
+int _open(const char *filename, int flags, ...);
 
 #define qemu_isalnum(c)                isalnum((unsigned char)(c))
 #define qemu_isalpha(c)                isalpha((unsigned char)(c))