Stop mutating the path in real fs functions

zerocc2014 · Nov 16, 2017 · 37aef44 · 37aef44
1 parent a58f8a8
commit 37aef44
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Showing 10 changed files with 63 additions and 72 deletions.
diff --git a/fs/path.c b/fs/path.c
@@ -21,9 +21,11 @@ int path_normalize(struct fd *at, const char *path, char *out, bool follow_links
             if (err < 0)
                 return err;
             assert(path_is_normalized(at_path));
-            strcpy(o, at_path);
-            n -= strlen(at_path);
-            o += strlen(at_path);
+            if (strcmp(at_path, "/") != 0) {
+                strcpy(o, at_path);
+                n -= strlen(at_path);
+                o += strlen(at_path);
+            }
         }
     }
 

diff --git a/fs/real.c b/fs/real.c
@@ -28,28 +28,19 @@ static int getpath(int fd, char *buf) {
 #endif
 }
 
-char *strnprepend(char *str, const char *prefix, size_t max) {
-    if (strlen(str) + strlen(prefix) + 1 > max)
-        return NULL;
-    const char *src = str + strlen(str) + 1;
-    char *dst = (char *) src + strlen(prefix);
-    while (src != str)
-        *dst-- = *src--;
-    *dst = *src;
-    src = prefix;
-    dst = str;
-    while (*src != '\0')
-        *dst++ = *src++;
-    return str;
+const char *fix_path(const char *path) {
+    if (strcmp(path, "/") == 0)
+        return ".";
+    if (path[0] == '/')
+        path++;
+    return path;
 }
 
 // TODO translate goddamn flags
 
-struct fd *realfs_open(struct mount *mount, char *path, int flags, int mode) {
-    if (strnprepend(path, mount->source, MAX_PATH) == NULL)
-        return ERR_PTR(_ENAMETOOLONG);
-
-    int fd_no = open(path, flags, mode);
+static struct fd *realfs_open(struct mount *mount, char *path, int flags, int mode) {
+    if (*path == '\0') path = ".";
+    int fd_no = openat(mount->root_fd, fix_path(path), flags, mode);
     if (fd_no < 0)
         return ERR_PTR(err_map(errno));
     struct fd *fd = fd_create();
@@ -93,16 +84,9 @@ static void copy_stat(struct statbuf *fake_stat, struct stat *real_stat) {
 }
 
 int realfs_stat(struct mount *mount, char *path, struct statbuf *fake_stat, bool follow_links) {
-    if (strnprepend(path, mount->source, MAX_PATH) == NULL)
-        return _ENAMETOOLONG;
-
     struct stat real_stat;
-    int (*stat_fn)(const char *path, struct stat *buf);
-    if (follow_links)
-        stat_fn = stat;
-    else
-        stat_fn = lstat;
-    if (stat_fn(path, &real_stat) < 0)
+    if (*path == '\0') path = ".";
+    if (fstatat(mount->root_fd, fix_path(path), &real_stat, follow_links ? 0 : AT_SYMLINK_NOFOLLOW) < 0)
         return err_map(errno);
     copy_stat(fake_stat, &real_stat);
     return 0;
@@ -116,26 +100,22 @@ int realfs_fstat(struct fd *fd, struct statbuf *fake_stat) {
     return 0;
 }
 
-int realfs_unlink(struct mount *mount, char *path) {
-    if (strnprepend(path, mount->source, MAX_PATH) == NULL)
-        return _ENAMETOOLONG;
-
-    int res = unlink(path);
+static int realfs_unlink(struct mount *mount, char *path) {
+    if (*path == '\0') path = ".";
+    int res = unlinkat(mount->root_fd, fix_path(path), 0);
     if (res < 0)
         return err_map(errno);
     return res;
 }
 
 int realfs_access(struct mount *mount, char *path, int mode) {
-    if (strnprepend(path, mount->source, MAX_PATH) == NULL)
-        return _ENAMETOOLONG;
-
     int real_mode = 0;
     if (mode & AC_F) real_mode |= F_OK;
     if (mode & AC_R) real_mode |= R_OK;
     if (mode & AC_W) real_mode |= W_OK;
     if (mode & AC_X) real_mode |= X_OK;
-    int res = access(path, real_mode);
+    if (*path == '\0') path = ".";
+    int res = faccessat(mount->root_fd, fix_path(path), real_mode, 0);
     if (res < 0)
         return err_map(errno);
     return res;
@@ -201,11 +181,9 @@ int realfs_mmap(struct fd *fd, off_t offset, size_t len, int prot, int flags, vo
     return 0;
 }
 
-ssize_t realfs_readlink(struct mount *mount, char *path, char *buf, size_t bufsize) {
-    if (strnprepend(path, mount->source, MAX_PATH) == NULL)
-        return _ENAMETOOLONG;
-
-    ssize_t size = readlink(path, buf, bufsize);
+static ssize_t realfs_readlink(struct mount *mount, char *path, char *buf, size_t bufsize) {
+    if (*path == '\0') path = ".";
+    ssize_t size = readlinkat(mount->root_fd, fix_path(path), buf, bufsize);
     if (size < 0)
         return err_map(errno);
     return size;
@@ -215,15 +193,10 @@ int realfs_getpath(struct fd *fd, char *buf) {
     int err = getpath(fd->real_fd, buf);
     if (err < 0)
         return err;
-    size_t source_len = strlen(fd->mount->source);
-    memmove(buf, buf + source_len, MAX_PATH - source_len);
-    return 0;
-}
-
-int realfs_statfs(struct mount *mount, struct statfsbuf *stat) {
-    stat->type = 0x7265616c;
-    stat->namelen = NAME_MAX;
-    stat->bsize = PAGE_SIZE;
+    if (strcmp(fd->mount->source, "/") != 0) {
+        size_t source_len = strlen(fd->mount->source);
+        memmove(buf, buf + source_len, MAX_PATH - source_len);
+    }
     return 0;
 }
 
@@ -236,14 +209,29 @@ int realfs_flock(struct fd *fd, int operation) {
     return flock(fd->real_fd, real_op);
 }
 
+int realfs_statfs(struct mount *mount, struct statfsbuf *stat) {
+    stat->type = 0x7265616c;
+    stat->namelen = NAME_MAX;
+    stat->bsize = PAGE_SIZE;
+    return 0;
+}
+
+int realfs_mount(struct mount *mount) {
+    mount->root_fd = open(mount->source, O_DIRECTORY);
+    if (mount->root_fd < 0)
+        return err_map(errno);
+    return 0;
+}
+
 const struct fs_ops realfs = {
+    .mount = realfs_mount,
+    .statfs = realfs_statfs,
     .open = realfs_open,
     .unlink = realfs_unlink,
     .stat = realfs_stat,
     .access = realfs_access,
     .readlink = realfs_readlink,
     .fstat = realfs_fstat,
-    .statfs = realfs_statfs,
     .flock = realfs_flock,
 };
 

diff --git a/kernel/fs.h b/kernel/fs.h
@@ -65,6 +65,8 @@ struct mount {
     const char *source;
     const struct fs_ops *fs;
     struct mount *next;
+
+    int root_fd;
     void *data;
 };
 extern struct mount *mounts;
@@ -76,6 +78,7 @@ extern struct mount *mounts;
 #define O_CREAT_ (1 << 6)
 
 struct fs_ops {
+    int (*mount)(struct mount *mount);
     int (*statfs)(struct mount *mount, struct statfsbuf *stat);
     // the path parameter points to MAX_PATH bytes of allocated memory, which
     // you can do whatever you want with (but make sure to return _ENAMETOOLONG
@@ -127,6 +130,7 @@ struct fd_ops {
 
 struct mount *find_mount(char *path);
 struct mount *find_mount_and_trim_path(char *path);
+const char *fix_path(const char *path); // TODO reconsider
 
 struct pollable {
     struct list fds;
@@ -172,7 +176,7 @@ void poll_destroy(struct poll *poll);
 //  - resolving . and ..
 //  - resolving symlinks, skipping the last path component if the follow_links
 //    argument is true
-// The result will always begin with a slash.
+// The result will always begin with a slash or be empty.
 //
 // If the normalized path plus the null terminator would be longer than
 // MAX_PATH, _ENAMETOOLONG is returned. The out buffer is expected to be at
@@ -183,12 +187,9 @@ bool path_is_normalized(const char *path);
 // real fs
 extern const struct fs_ops realfs;
 
-struct fd *realfs_open(struct mount *mount, char *path, int flags, int mode);
 int realfs_stat(struct mount *mount, char *path, struct statbuf *fake_stat, bool follow_links);
 int realfs_fstat(struct fd *fd, struct statbuf *fake_stat);
-int realfs_unlink(struct mount *mount, char *path);
 int realfs_access(struct mount *mount, char *path, int mode);
-ssize_t realfs_readlink(struct mount *mount, char *path, char *buf, size_t bufsize);
 int realfs_statfs(struct mount *mount, struct statfsbuf *stat);
 int realfs_flock(struct fd *fd, int operation);
 extern const struct fd_ops realfs_fdops;
@@ -202,7 +203,4 @@ struct fd *adhoc_fd_create(void);
 // fake fs
 extern const struct fs_ops fakefs;
 
-// TODO put this somewhere else
-char *strnprepend(char *str, const char *prefix, size_t max);
-
 #endif
diff --git a/kernel/init.c b/kernel/init.c
@@ -15,6 +15,11 @@ int mount_root(const struct fs_ops *fs, const char *source) {
     mounts->fs = fs;
     mounts->next = NULL;
     mounts->data = NULL;
+    if (fs->mount) {
+        int err = fs->mount(mounts);
+        if (err < 0)
+            return err;
+    }
     return 0;
 }
 

diff --git a/main.c b/main.c
@@ -5,7 +5,9 @@
 
 int main(int argc, char *const argv[]) {
     int err = xX_main_Xx(argc, argv);
-    if (err < 0)
+    if (err < 0) {
+        fprintf(stderr, "%s\n", strerror(-err));
         return err;
+    }
     cpu_run(&current->cpu);
 }
diff --git a/tools/ptraceomatic.c b/tools/ptraceomatic.c
@@ -442,12 +442,9 @@ int main(int argc, char *const argv[]) {
         fprintf(stderr, "enametoolong\n"); exit(1);
     }
     struct mount *mount = find_mount_and_trim_path(exec_path);
-    if (strnprepend(exec_path, mount->source, MAX_PATH) == NULL) {
-        fprintf(stderr, "enametoolong\n"); exit(1);
-    }
     int fds[2];
     trycall(socketpair(AF_UNIX, SOCK_DGRAM, 0, fds), "socketpair");
-    int pid = start_tracee(exec_path, argv + optind, (char *[]) {NULL});
+    int pid = start_tracee(mount->root_fd, exec_path, argv + optind, (char *[]) {NULL});
     int sender = fds[0], receiver = fds[1];
     /* close(receiver); // only needed in the child */
     prepare_tracee(pid);

diff --git a/tools/ptutil.c b/tools/ptutil.c
@@ -25,7 +25,7 @@ static int arch_prctl(int code, unsigned long arg) {
     return syscall(SYS_arch_prctl, code, arg);
 }
 
-int start_tracee(const char *path, char *const argv[], char *const envp[]) {
+int start_tracee(int at, const char *path, char *const argv[], char *const envp[]) {
     // shut off aslr
     int persona = personality(0xffffffff);
     persona |= ADDR_NO_RANDOMIZE;
@@ -42,7 +42,7 @@ int start_tracee(const char *path, char *const argv[], char *const envp[]) {
         trycall(prctl(PR_SET_TSC, PR_TSC_SIGSEGV), "rdtsc faulting");
         /* trycall(arch_prctl(ARCH_SET_CPUID, 0), "cpuid faulting"); */
         trycall(ptrace(PTRACE_TRACEME, 0, NULL, NULL), "ptrace traceme");
-        trycall(execve(path, argv, envp), "fexecve");
+        trycall(syscall(SYS_execveat, at, path, argv, envp, 0), "fexecve");
     } else {
         // parent, wait for child to stop after exec
         int status;

diff --git a/tools/ptutil.h b/tools/ptutil.h
@@ -1,7 +1,7 @@
 #include "../misc.h"
 
 long trycall(long res, const char *msg);
-int start_tracee(const char *path, char *const argv[], char *const envp[]);
+int start_tracee(int at, const char *path, char *const argv[], char *const envp[]);
 int open_mem(int pid);
 dword_t pt_read(int pid, addr_t addr);
 void pt_write8(int pid, addr_t addr, byte_t val);

diff --git a/tools/vdso-transplant-main.c b/tools/vdso-transplant-main.c
@@ -18,7 +18,7 @@
 
 int main(int argc, char *const argv[]) {
     char *const envp[] = {NULL};
-    int pid = start_tracee(argv[2], argv + 2, envp);
+    int pid = start_tracee(AT_FDCWD, argv[2], argv + 2, envp);
 
     int vdso_fd = trycall(open(argv[1], O_RDONLY), "open vdso");
     struct stat statbuf;

diff --git a/xX_main_Xx.h b/xX_main_Xx.h
@@ -44,8 +44,7 @@ static inline int xX_main_Xx(int argc, char *const argv[]) {
         current->pwd = pwd;
     }
 
-    char *envp[] = {NULL};
-    int err = sys_execve(argv[optind], argv + optind, envp);
+    int err = sys_execve(argv[optind], argv + optind, (char *[]) {NULL});
     if (err < 0)
         return err;
     err = create_stdio(real_tty_driver);