A tar file created by toybox tar with values large enough to need base-256 rather than ASCII octal caused a tar reader to crash, and caused GNU tar to complain.
I note from the docs at https://github.com/libarchive/libarchive/blob/master/libarchive/tar.5#L326 that they imply that only the top *bit* should be set to indicate this format, not the whole top byte, to give a 95-bit or 63-bit field. But I don't think we can hit that in practice? Bug: http://b/181683612 --- tests/tar.test | 5 +++++ toys/posix/tar.c | 17 ++++++++++++----- 2 files changed, 17 insertions(+), 5 deletions(-)
From ba28a4450e306fa16678a2703960b582671528ed Mon Sep 17 00:00:00 2001 From: Elliott Hughes <[email protected]> Date: Mon, 8 Mar 2021 09:47:54 -0800 Subject: [PATCH] tar: fix base-256 output. A tar file created by toybox tar with values large enough to need base-256 rather than ASCII octal caused a tar reader to crash, and caused GNU tar to complain. I note from the docs at https://github.com/libarchive/libarchive/blob/master/libarchive/tar.5#L326 that they imply that only the top *bit* should be set to indicate this format, not the whole top byte, to give a 95-bit or 63-bit field. But I don't think we can hit that in practice? Bug: http://b/181683612 --- tests/tar.test | 5 +++++ toys/posix/tar.c | 17 ++++++++++++----- 2 files changed, 17 insertions(+), 5 deletions(-) diff --git a/tests/tar.test b/tests/tar.test index 4b2f2120..70668c9c 100644 --- a/tests/tar.test +++ b/tests/tar.test @@ -59,6 +59,11 @@ skipnot id nobody >/dev/null testing "pass group" "tar c --owner root --group nobody --mtime @0 file | LST" \ "-rw-rw-r-- root/nobody 0 1970-01-01 00:00 file\n" "" "" +# Historically we output a "base 256" format that _we_ could decode but that +# GNU tar choked on, so check the exact bytes with SUM, not a LST round trip. +testing "huge values" "tar c --owner 9999999 --group 8888888 --mtime @0 file | SUM 3" \ + "396b07fd2f80eeb312462e3bfb7dc1325dc6bcfb\n" "" "" + touch -t 198701231234.56 file testing "pass mtime" \ "tar c --owner root --group root file | LST --full-time" \ diff --git a/toys/posix/tar.c b/toys/posix/tar.c index f31640c5..25dfc167 100644 --- a/toys/posix/tar.c +++ b/toys/posix/tar.c @@ -85,14 +85,19 @@ struct tar_hdr { prefix[155], padd[12]; }; +// Tar uses ASCII octal when it fits, base-256 otherwise. +#define ASCII_FITS(val, len) (!(val>>(3*(len-1)))) // convert from int to octal (or base-256) static void itoo(char *str, int len, unsigned long long val) { - // Do we need binary encoding? - if (!(val>>(3*(len-1)))) sprintf(str, "%0*llo", len-1, val); + if (ASCII_FITS(val, len)) sprintf(str, "%0*llo", len-1, val); else { + str += len; + while (len--) { + *--str = val; + val >>= 8; + } *str = 128; - while (--len) *++str = val>>(3*len); } } #define ITOO(x, y) itoo(x, sizeof(x), y) @@ -288,9 +293,11 @@ static int add_to_tar(struct dirtree *node) if (strlen(hname) > sizeof(hdr.name)) write_longname(hname, 'L'); if (!FLAG(numeric_owner)) { - if (TT.owner || (pw = bufgetpwuid(st->st_uid))) + if ((TT.owner || (pw = bufgetpwuid(st->st_uid))) && + ASCII_FITS(st->st_uid, sizeof(hdr.uid))) strncpy(hdr.uname, TT.owner ? TT.owner : pw->pw_name, sizeof(hdr.uname)); - if (TT.group || (gr = bufgetgrgid(st->st_gid))) + if ((TT.group || (gr = bufgetgrgid(st->st_gid))) && + ASCII_FITS(st->st_gid, sizeof(hdr.gid))) strncpy(hdr.gname, TT.group ? TT.group : gr->gr_name, sizeof(hdr.gname)); } -- 2.30.1.766.gb4fecdf3b7-goog
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