tar: optional support for restoring selinux context

function                                             old     new   delta
get_header_tar                                      1690    1976    +286
data_extract_all                                     821     881     +60
.rodata                                           151446  151503     +57
get_header_cpio                                     1044    1077     +33
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/0 up/down: 436/0)             Total: 436 bytes

Signed-off-by: J. Tang <tang@jtang.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/archival/Config.in b/archival/Config.in
index c99896b477568d6339332558579421870789a117..deacc28222289afc1250fd009e0ee973461c52c9 100644 (file)
--- a/archival/Config.in
+++ b/archival/Config.in
@@ -289,6 +289,14 @@ config FEATURE_TAR_NOPRESERVE_TIME
          With this option busybox supports GNU tar -m
          (do not preserve time) option.
 
+config FEATURE_TAR_SELINUX
+       bool "Support for extracting SELinux labels"
+       default n
+       depends on TAR && SELINUX
+       help
+         With this option busybox supports restoring SELinux labels
+         when extracting files from tar archives.
+
 config UNCOMPRESS
        bool "uncompress"
        default n

diff --git a/archival/libunarchive/data_extract_all.c b/archival/libunarchive/data_extract_all.c
index 58b05335b0969cc006e2af4a989dfa0685d43c3a..cc4894229b5e7ba6ec24d91aebf7cc9f9c4f9515 100644 (file)
--- a/archival/libunarchive/data_extract_all.c
+++ b/archival/libunarchive/data_extract_all.c
@@ -12,6 +12,17 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
        int dst_fd;
        int res;
 
+#if ENABLE_FEATURE_TAR_SELINUX
+       char *sctx = archive_handle->tar__next_file_sctx;
+       if (!sctx)
+               sctx = archive_handle->tar__global_sctx;
+       if (sctx) { /* setfscreatecon is 4 syscalls, avoid if possible */
+               setfscreatecon(sctx);
+               free(archive_handle->tar__next_file_sctx);
+               archive_handle->tar__next_file_sctx = NULL;
+       }
+#endif
+
        if (archive_handle->ah_flags & ARCHIVE_CREATE_LEADING_DIRS) {
                char *slash = strrchr(file_header->name, '/');
                if (slash) {
@@ -45,7 +56,7 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
                                        "same age file exists", file_header->name);
                        }
                        data_skip(archive_handle);
-                       return;
+                       goto ret;
                }
                else if ((unlink(file_header->name) == -1) && (errno != EISDIR)) {
                        bb_perror_msg_and_die("can't remove old file %s",
@@ -158,4 +169,12 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
                        utimes(file_header->name, t);
                }
        }
+
+ ret: ;
+#if ENABLE_FEATURE_TAR_SELINUX
+       if (sctx) {
+               /* reset the context after creating an entry */
+               setfscreatecon(NULL);
+       }
+#endif
 }

diff --git a/archival/libunarchive/get_header_tar.c b/archival/libunarchive/get_header_tar.c
index d5b86ff5c4704720d4217ed98bb668668eba2b5a..cf0b9ab028a00c248ca9fe0d2e85e4a6b14281b1 100644 (file)
--- a/archival/libunarchive/get_header_tar.c
+++ b/archival/libunarchive/get_header_tar.c
@@ -103,6 +103,63 @@ static unsigned long long getOctal(char *str, int len)
 }
 #define GET_OCTAL(a) getOctal((a), sizeof(a))
 
+#if ENABLE_FEATURE_TAR_SELINUX
+/* Scan a PAX header for SELinux contexts, via "RHT.security.selinux" keyword.
+ * This is what Red Hat's patched version of tar uses.
+ */
+# define SELINUX_CONTEXT_KEYWORD "RHT.security.selinux"
+static char *get_selinux_sctx_from_pax_hdr(archive_handle_t *archive_handle, unsigned sz)
+{
+       char *buf, *p;
+       char *result;
+
+       p = buf = xmalloc(sz + 1);
+       /* prevent bb_strtou from running off the buffer */
+       buf[sz] = '\0';
+       xread(archive_handle->src_fd, buf, sz);
+       archive_handle->offset += sz;
+
+       result = NULL;
+       while (sz != 0) {
+               char *end, *value;
+               unsigned len;
+
+               /* Every record has this format: "LEN NAME=VALUE\n" */
+               len = bb_strtou(p, &end, 10);
+               /* expect errno to be EINVAL, because the character
+                * following the digits should be a space
+                */
+               p += len;
+               sz -= len;
+               if ((int)sz < 0
+                || len == 0
+                || errno != EINVAL
+                || *end != ' '
+               ) {
+                       bb_error_msg("malformed extended header, skipped");
+                       // More verbose version:
+                       //bb_error_msg("malformed extended header at %"OFF_FMT"d, skipped",
+                       //              archive_handle->offset - (sz + len));
+                       break;
+               }
+               /* overwrite the terminating newline with NUL
+                * (we do not bother to check that it *was* a newline)
+                */
+               p[-1] = '\0';
+               /* Is it selinux security context? */
+               value = end + 1;
+               if (strncmp(value, SELINUX_CONTEXT_KEYWORD"=", sizeof(SELINUX_CONTEXT_KEYWORD"=") - 1) == 0) {
+                       value += sizeof(SELINUX_CONTEXT_KEYWORD"=") - 1;
+                       result = xstrdup(value);
+                       break;
+               }
+       }
+
+       free(buf);
+       return result;
+}
+#endif
+
 void BUG_tar_header_size(void);
 char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
 {
@@ -150,7 +207,7 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
        if (sizeof(tar) != 512)
                BUG_tar_header_size();
 
-#if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
+#if ENABLE_FEATURE_TAR_GNU_EXTENSIONS || ENABLE_FEATURE_TAR_SELINUX
  again:
 #endif
        /* Align header */
@@ -392,8 +449,13 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
        case 'S':       /* Sparse file */
        case 'V':       /* Volume header */
 #endif
+#if !ENABLE_FEATURE_TAR_SELINUX
        case 'g':       /* pax global header */
-       case 'x': {     /* pax extended header */
+       case 'x':       /* pax extended header */
+#else
+ skip_ext_hdr:
+#endif
+       {
                off_t sz;
                bb_error_msg("warning: skipping header '%c'", tar.typeflag);
                sz = (file_header->size + 511) & ~(off_t)511;
@@ -404,6 +466,18 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
                /* return get_header_tar(archive_handle); */
                goto again_after_align;
        }
+#if ENABLE_FEATURE_TAR_SELINUX
+       case 'g':       /* pax global header */
+       case 'x': {     /* pax extended header */
+               char **pp;
+               if ((uoff_t)file_header->size > 0xfffff) /* paranoia */
+                       goto skip_ext_hdr;
+               pp = (tar.typeflag == 'g') ? &archive_handle->tar__global_sctx : &archive_handle->tar__next_file_sctx;
+               free(*pp);
+               *pp = get_selinux_sctx_from_pax_hdr(archive_handle, file_header->size);
+               goto again;
+       }
+#endif
        default:
                bb_error_msg_and_die("unknown typeflag: 0x%x", tar.typeflag);
        }

diff --git a/include/unarchive.h b/include/unarchive.h
index 92ebd656548654d9e72d90e01dc3060fe16ccfa6..a834816ba289f4f2ac627ffea2597cf356cab10d 100644 (file)
--- a/include/unarchive.h
+++ b/include/unarchive.h
@@ -59,6 +59,10 @@ typedef struct archive_handle_t {
        char* tar__longname;
        char* tar__linkname;
 # endif
+# if ENABLE_FEATURE_TAR_SELINUX
+       char* tar__global_sctx;
+       char* tar__next_file_sctx;
+# endif
 #endif
 #if ENABLE_CPIO || ENABLE_RPM2CPIO || ENABLE_RPM
        uoff_t cpio__blocks;