git: fix CVE-2021-21300

checkout: fix bug that makes checkout follow symlinks in leading path

Upstream-Status: Acepted [https://github.com/git/git/commit/684dd4c2b414bcf648505e74498a608f28de4592]
CVE: CVE-2021-21300
(From OE-Core rev: 8293d5d1529629bd13028bdde1fa99da30313bac)

Signed-off-by: Minjae Kim <flowergom@gmail.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

2 files changed, 308 insertions, 1 deletions

diff --git a/meta/recipes-devtools/git/files/CVE-2021-21300.patch b/meta/recipes-devtools/git/files/CVE-2021-21300.patch
new file mode 100644
index 0000000000..9206f711cf
--- /dev/null
+++ b/meta/recipes-devtools/git/files/CVE-2021-21300.patch
@@ -0,0 +1,305 @@
+From 0e9cef2414f0df3fa5b9b56ff9072aa122bef29c Mon Sep 17 00:00:00 2001
+From: Minjae Kim <flowrgom@gmail.com>
+Date: Sat, 27 Mar 2021 15:18:46 +0900
+Subject: [PATCH] checkout: fix bug that makes checkout follow symlinks in
+ leading path
+
+Before checking out a file, we have to confirm that all of its leading
+components are real existing directories. And to reduce the number of
+lstat() calls in this process, we cache the last leading path known to
+contain only directories. However, when a path collision occurs (e.g.
+when checking out case-sensitive files in case-insensitive file
+systems), a cached path might have its file type changed on disk,
+leaving the cache on an invalid state. Normally, this doesn't bring
+any bad consequences as we usually check out files in index order, and
+therefore, by the time the cached path becomes outdated, we no longer
+need it anyway (because all files in that directory would have already
+been written).
+
+But, there are some users of the checkout machinery that do not always
+follow the index order. In particular: checkout-index writes the paths
+in the same order that they appear on the CLI (or stdin); and the
+delayed checkout feature -- used when a long-running filter process
+replies with "status=delayed" -- postpones the checkout of some entries,
+thus modifying the checkout order.
+
+When we have to check out an out-of-order entry and the lstat() cache is
+invalid (due to a previous path collision), checkout_entry() may end up
+using the invalid data and thrusting that the leading components are
+real directories when, in reality, they are not. In the best case
+scenario, where the directory was replaced by a regular file, the user
+will get an error: "fatal: unable to create file 'foo/bar': Not a
+directory". But if the directory was replaced by a symlink, checkout
+could actually end up following the symlink and writing the file at a
+wrong place, even outside the repository. Since delayed checkout is
+affected by this bug, it could be used by an attacker to write
+arbitrary files during the clone of a maliciously crafted repository.
+
+Some candidate solutions considered were to disable the lstat() cache
+during unordered checkouts or sort the entries before passing them to
+the checkout machinery. But both ideas include some performance penalty
+and they don't future-proof the code against new unordered use cases.
+
+Instead, we now manually reset the lstat cache whenever we successfully
+remove a directory. Note: We are not even checking whether the directory
+was the same as the lstat cache points to because we might face a
+scenario where the paths refer to the same location but differ due to
+case folding, precomposed UTF-8 issues, or the presence of `..`
+components in the path. Two regression tests, with case-collisions and
+utf8-collisions, are also added for both checkout-index and delayed
+checkout.
+
+Note: to make the previously mentioned clone attack unfeasible, it would
+be sufficient to reset the lstat cache only after the remove_subtree()
+call inside checkout_entry(). This is the place where we would remove a
+directory whose path collides with the path of another entry that we are
+currently trying to check out (possibly a symlink). However, in the
+interest of a thorough fix that does not leave Git open to
+similar-but-not-identical attack vectors, we decided to intercept
+all `rmdir()` calls in one fell swoop.
+
+This addresses CVE-2021-21300.
+
+Co-authored-by: Johannes Schindelin <johannes.schindelin@gmx.de>
+Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
+
+Upstream-Status: Acepted [https://github.com/git/git/commit/684dd4c2b414bcf648505e74498a608f28de4592]
+CVE: CVE-2021-21300
+Signed-off-by: Minjae Kim <flowergom@gmail.com>
+---
+ cache.h                         |  1 +
+ compat/mingw.c                  |  2 ++
+ git-compat-util.h               |  5 +++++
+ symlinks.c                      | 25 +++++++++++++++++++++
+ t/t0021-conversion.sh           | 39 ++++++++++++++++++++++++++++++++
+ t/t0021/rot13-filter.pl         | 21 ++++++++++++++---
+ t/t2006-checkout-index-basic.sh | 40 +++++++++++++++++++++++++++++++++
+ 7 files changed, 130 insertions(+), 3 deletions(-)
+
+diff --git a/cache.h b/cache.h
+index 04cabaa..dda373f 100644
+--- a/cache.h
++++ b/cache.h
+@@ -1675,6 +1675,7 @@ int has_symlink_leading_path(const char *name, int len);
+ int threaded_has_symlink_leading_path(struct cache_def *, const char *, int);
+ int check_leading_path(const char *name, int len);
+ int has_dirs_only_path(const char *name, int len, int prefix_len);
++extern void invalidate_lstat_cache(void);
+ void schedule_dir_for_removal(const char *name, int len);
+ void remove_scheduled_dirs(void);
+ 
+diff --git a/compat/mingw.c b/compat/mingw.c
+index bd24d91..cea9c72 100644
+--- a/compat/mingw.c
++++ b/compat/mingw.c
+@@ -340,6 +340,8 @@ int mingw_rmdir(const char *pathname)
+               ask_yes_no_if_possible("Deletion of directory '%s' failed. "
+                        "Should I try again?", pathname))
+               ret = _wrmdir(wpathname);
++       if (!ret)
++               invalidate_lstat_cache();
+        return ret;
+ }
+ 
+diff --git a/git-compat-util.h b/git-compat-util.h
+index d0dd9c0..a1ecfd3 100644
+--- a/git-compat-util.h
++++ b/git-compat-util.h
+@@ -365,6 +365,11 @@ static inline int noop_core_config(const char *var, const char *value, void *cb)
+ #define platform_core_config noop_core_config
+ #endif
+ 
++int lstat_cache_aware_rmdir(const char *path);
++#if !defined(__MINGW32__) && !defined(_MSC_VER)
++#define rmdir lstat_cache_aware_rmdir
++#endif
++
+ #ifndef has_dos_drive_prefix
+ static inline int git_has_dos_drive_prefix(const char *path)
+ {
+diff --git a/symlinks.c b/symlinks.c
+index 69d458a..ae3c665 100644
+--- a/symlinks.c
++++ b/symlinks.c
+@@ -267,6 +267,13 @@ int has_dirs_only_path(const char *name, int len, int prefix_len)
+  */
+ static int threaded_has_dirs_only_path(struct cache_def *cache, const char *name, int len, int prefix_len)
+ {
++       /*
++        * Note: this function is used by the checkout machinery, which also
++        * takes care to properly reset the cache when it performs an operation
++        * that would leave the cache outdated. If this function starts caching
++        * anything else besides FL_DIR, remember to also invalidate the cache
++        * when creating or deleting paths that might be in the cache.
++        */
+        return lstat_cache(cache, name, len,
+                           FL_DIR|FL_FULLPATH, prefix_len) &
+                FL_DIR;
+@@ -321,3 +328,21 @@ void remove_scheduled_dirs(void)
+ {
+        do_remove_scheduled_dirs(0);
+ }
++
++
++void invalidate_lstat_cache(void)
++{
++       reset_lstat_cache(&default_cache);
++}
++
++#undef rmdir
++int lstat_cache_aware_rmdir(const char *path)
++{
++       /* Any change in this function must be made also in `mingw_rmdir()` */
++       int ret = rmdir(path);
++
++       if (!ret)
++               invalidate_lstat_cache();
++
++       return ret;
++}
+diff --git a/t/t0021-conversion.sh b/t/t0021-conversion.sh
+index c954c70..6a1d5f6 100755
+--- a/t/t0021-conversion.sh
++++ b/t/t0021-conversion.sh
+@@ -820,4 +820,43 @@ test_expect_success PERL 'invalid file in delayed checkout' '
+        grep "error: external filter .* signaled that .unfiltered. is now available although it has not been delayed earlier" git-stderr.log
+ '
+ 
++for mode in 'case' 'utf-8'
++do
++       case "$mode" in
++       case)   dir='A' symlink='a' mode_prereq='CASE_INSENSITIVE_FS' ;;
++       utf-8)
++               dir=$(printf "\141\314\210") symlink=$(printf "\303\244")
++               mode_prereq='UTF8_NFD_TO_NFC' ;;
++       esac
++
++       test_expect_success PERL,SYMLINKS,$mode_prereq \
++       "delayed checkout with $mode-collision don't write to the wrong place" '
++               test_config_global filter.delay.process \
++                       "\"$TEST_ROOT/rot13-filter.pl\" --always-delay delayed.log clean smudge delay" &&
++               test_config_global filter.delay.required true &&
++               git init $mode-collision &&
++               (
++                       cd $mode-collision &&
++                       mkdir target-dir &&
++                       empty_oid=$(printf "" | git hash-object -w --stdin) &&
++                       symlink_oid=$(printf "%s" "$PWD/target-dir" | git hash-object -w --stdin) &&
++                       attr_oid=$(echo "$dir/z filter=delay" | git hash-object -w --stdin) &&
++                       cat >objs <<-EOF &&
++                       100644 blob $empty_oid  $dir/x
++                       100644 blob $empty_oid  $dir/y
++                       100644 blob $empty_oid  $dir/z
++                       120000 blob $symlink_oid        $symlink
++                       100644 blob $attr_oid   .gitattributes
++                       EOF
++                       git update-index --index-info <objs &&
++                       git commit -m "test commit"
++               ) &&
++               git clone $mode-collision $mode-collision-cloned &&
++               # Make sure z was really delayed
++               grep "IN: smudge $dir/z .* \\[DELAYED\\]" $mode-collision-cloned/delayed.log &&
++               # Should not create $dir/z at $symlink/z
++               test_path_is_missing $mode-collision/target-dir/z
++       '
++done
++
+ test_done
+diff --git a/t/t0021/rot13-filter.pl b/t/t0021/rot13-filter.pl
+index 4701072..007f2d7 100644
+--- a/t/t0021/rot13-filter.pl
++++ b/t/t0021/rot13-filter.pl
+@@ -2,9 +2,15 @@
+ # Example implementation for the Git filter protocol version 2
+ # See Documentation/gitattributes.txt, section "Filter Protocol"
+ #
+-# The first argument defines a debug log file that the script write to.
+-# All remaining arguments define a list of supported protocol
+-# capabilities ("clean", "smudge", etc).
++# Usage: rot13-filter.pl [--always-delay] <log path> <capabilities>
++#
++# Log path defines a debug log file that the script writes to. The
++# subsequent arguments define a list of supported protocol capabilities
++# ("clean", "smudge", etc).
++#
++# When --always-delay is given all pathnames with the "can-delay" flag
++# that don't appear on the list bellow are delayed with a count of 1
++# (see more below).
+ #
+ # This implementation supports special test cases:
+ # (1) If data with the pathname "clean-write-fail.r" is processed with
+@@ -53,6 +59,13 @@ sub gitperllib {
+ use Git::Packet;
+ 
+ my $MAX_PACKET_CONTENT_SIZE = 65516;
++
++my $always_delay = 0;
++if ( $ARGV[0] eq '--always-delay' ) {
++       $always_delay = 1;
++       shift @ARGV;
++}
++
+ my $log_file                = shift @ARGV;
+ my @capabilities            = @ARGV;
+ 
+@@ -134,6 +147,8 @@ sub rot13 {
+                        if ( $buffer eq "can-delay=1" ) {
+                                if ( exists $DELAY{$pathname} and $DELAY{$pathname}{"requested"} == 0 ) {
+                                        $DELAY{$pathname}{"requested"} = 1;
++                               } elsif ( !exists $DELAY{$pathname} and $always_delay ) {
++                                       $DELAY{$pathname} = { "requested" => 1, "count" => 1 };
+                                }
+                        } else {
+                                die "Unknown message '$buffer'";
+diff --git a/t/t2006-checkout-index-basic.sh b/t/t2006-checkout-index-basic.sh
+index 57cbdfe..f223a02 100755
+--- a/t/t2006-checkout-index-basic.sh
++++ b/t/t2006-checkout-index-basic.sh
+@@ -21,4 +21,44 @@ test_expect_success 'checkout-index -h in broken repository' '
+        test_i18ngrep "[Uu]sage" broken/usage
+ '
+ 
++for mode in 'case' 'utf-8'
++do
++       case "$mode" in
++       case)   dir='A' symlink='a' mode_prereq='CASE_INSENSITIVE_FS' ;;
++       utf-8)
++               dir=$(printf "\141\314\210") symlink=$(printf "\303\244")
++               mode_prereq='UTF8_NFD_TO_NFC' ;;
++       esac
++
++       test_expect_success SYMLINKS,$mode_prereq \
++       "checkout-index with $mode-collision don't write to the wrong place" '
++               git init $mode-collision &&
++               (
++                       cd $mode-collision &&
++                       mkdir target-dir &&
++                       empty_obj_hex=$(git hash-object -w --stdin </dev/null) &&
++                       symlink_hex=$(printf "%s" "$PWD/target-dir" | git hash-object -w --stdin) &&
++                       cat >objs <<-EOF &&
++                       100644 blob ${empty_obj_hex}    ${dir}/x
++                       100644 blob ${empty_obj_hex}    ${dir}/y
++                       100644 blob ${empty_obj_hex}    ${dir}/z
++                       120000 blob ${symlink_hex}      ${symlink}
++                       EOF
++                       git update-index --index-info <objs &&
++                       # Note: the order is important here to exercise the
++                       # case where the file at ${dir} has its type changed by
++                       # the time Git tries to check out ${dir}/z.
++                       #
++                       # Also, we use core.precomposeUnicode=false because we
++                       # want Git to treat the UTF-8 paths transparently on
++                       # Mac OS, matching what is in the index.
++                       #
++                       git -c core.precomposeUnicode=false checkout-index -f \
++                               ${dir}/x ${dir}/y ${symlink} ${dir}/z &&
++                       # Should not create ${dir}/z at ${symlink}/z
++                       test_path_is_missing target-dir/z
++               )
++       '
++done
++
+ test_done
+-- 
+2.17.1
+
diff --git a/meta/recipes-devtools/git/git.inc b/meta/recipes-devtools/git/git.inc
index ae463061d8..738a429875 100644
--- a/meta/recipes-devtools/git/git.inc
+++ b/meta/recipes-devtools/git/git.inc
@@ -8,7 +8,9 @@ DEPENDS = "openssl curl zlib expat"
 PROVIDES_append_class-native = " git-replacement-native"
 
 SRC_URI = "${KERNELORG_MIRROR}/software/scm/git/git-${PV}.tar.gz;name=tarball \
-           ${KERNELORG_MIRROR}/software/scm/git/git-manpages-${PV}.tar.gz;name=manpages"
+           ${KERNELORG_MIRROR}/software/scm/git/git-manpages-${PV}.tar.gz;name=manpages \
+           file://CVE-2021-21300.patch \
+"
 
 S = "${WORKDIR}/git-${PV}"