efivars: efivarfs_valid_name() should handle pstore syntax

Stricter validation was introduced with commit da27a24383b2b
("efivarfs: guid part of filenames are case-insensitive") and commit
47f531e8ba3b ("efivarfs: Validate filenames much more aggressively"),
which is necessary for the guid portion of efivarfs filenames, but we
don't need to be so strict with the first part, the variable name. The
UEFI specification doesn't impose any constraints on variable names
other than they be a NULL-terminated string.

The above commits caused a regression that resulted in users seeing
the following message,

$ sudo mount -v /sys/firmware/efi/efivars mount: Cannot allocate memory

whenever pstore EFI variables were present in the variable store,
since their variable names failed to pass the following check,

/* GUID should be right after the first '-' */
if (s - 1 != strchr(str, '-'))

as a typical pstore filename is of the form, dump-type0-10-1-<guid>.
The fix is trivial since the guid portion of the filename is GUID_LEN
bytes, we can use (len - GUID_LEN) to ensure the '-' character is
where we expect it to be.

(The bogus ENOMEM error value will be fixed in a separate patch.)

Reported-by: Joseph Yasi <[e-mail]>
Tested-by: Joseph Yasi <[e-mail]>
Reported-by: Lingzhu Xiang <[e-mail]>
Cc: Josh Boyer <[e-mail]>
Cc: Jeremy Kerr <[e-mail]>
Cc: Matthew Garrett <[e-mail]>
Cc: <[e-mail]> # v3.8
Signed-off-by: Matt Fleming <[e-mail]>

drivers/firmware/efivars.c

···
 	if (len < GUID_LEN + 2)
 		return false;
 
-	/* GUID should be right after the first '-' */
-	if (s - 1 != strchr(str, '-'))
+	/* GUID must be preceded by a '-' */
+	if (*(s - 1) != '-')
 		return false;
 
 	/*

tools/testing/selftests/efivarfs/efivarfs.sh

···
 	./open-unlink $file
 }
 
+# test that we can create a range of filenames
+test_valid_filenames()
+{
+	local attrs='\x07\x00\x00\x00'
+	local ret=0
+
+	local file_list="abc dump-type0-11-1-1362436005 1234 -"
+	for f in $file_list; do
+		local file=$efivarfs_mount/$f-$test_guid
+
+		printf "$attrs\x00" > $file
+
+		if [ ! -e $file ]; then
+			echo "$file could not be created" >&2
+			ret=1
+		else
+			rm $file
+		fi
+	done
+
+	exit $ret
+}
+
+test_invalid_filenames()
+{
+	local attrs='\x07\x00\x00\x00'
+	local ret=0
+
+	local file_list="
+		-1234-1234-1234-123456789abc
+		foo
+		foo-bar
+		-foo-
+		foo-barbazba-foob-foob-foob-foobarbazfoo
+		foo-------------------------------------
+		-12345678-1234-1234-1234-123456789abc
+		a-12345678=1234-1234-1234-123456789abc
+		a-12345678-1234=1234-1234-123456789abc
+		a-12345678-1234-1234=1234-123456789abc
+		a-12345678-1234-1234-1234=123456789abc
+		1112345678-1234-1234-1234-123456789abc"
+
+	for f in $file_list; do
+		local file=$efivarfs_mount/$f
+
+		printf "$attrs\x00" 2>/dev/null > $file
+
+		if [ -e $file ]; then
+			echo "Creating $file should have failed" >&2
+			rm $file
+			ret=1
+		fi
+	done
+
+	exit $ret
+}
+
 check_prereqs
 
 rc=0
···
 run_test test_delete
 run_test test_zero_size_delete
 run_test test_open_unlink
+run_test test_valid_filenames
+run_test test_invalid_filenames
 
 exit $rc