[xen staging] xz: validate the value before assigning it to an enum variable

[patchbot@xxxxxxx]

commit 0a21660515c24f09c4ee060ce0bb42e4b2e6b6fa
Author:     Lasse Collin <lasse.collin@xxxxxxxxxxx>
AuthorDate: Mon Mar 7 09:08:54 2022 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Mar 7 09:08:54 2022 +0100

    xz: validate the value before assigning it to an enum variable
    
    This might matter, for example, if the underlying type of enum xz_check
    was a signed char. In such a case the validation wouldn't have caught an
    unsupported header. I don't know if this problem can occur in the kernel
    on any arch but it's still good to fix it because some people might copy
    the XZ code to their own projects from Linux instead of the upstream
    XZ Embedded repository.
    
    This change may increase the code size by a few bytes. An alternative
    would have been to use an unsigned int instead of enum xz_check but
    using an enumeration looks cleaner.
    
    Link: https://lore.kernel.org/r/20211010213145.17462-3-xiang@xxxxxxxxxx
    Signed-off-by: Lasse Collin <lasse.collin@xxxxxxxxxxx>
    Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
    Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 
4f8d7abaa413
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/common/xz/dec_stream.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/common/xz/dec_stream.c b/xen/common/xz/dec_stream.c
index 672c57fac9..b91d8362c1 100644
--- a/xen/common/xz/dec_stream.c
+++ b/xen/common/xz/dec_stream.c
@@ -402,12 +402,12 @@ static enum xz_ret __init dec_stream_header(struct xz_dec 
*s)
         * we will accept other check types too, but then the check won't
         * be verified and a warning (XZ_UNSUPPORTED_CHECK) will be given.
         */
+       if (s->temp.buf[HEADER_MAGIC_SIZE + 1] > XZ_CHECK_MAX)
+               return XZ_OPTIONS_ERROR;
+
        s->check_type = s->temp.buf[HEADER_MAGIC_SIZE + 1];
 
 #ifdef XZ_DEC_ANY_CHECK
-       if (s->check_type > XZ_CHECK_MAX)
-               return XZ_OPTIONS_ERROR;
-
        if (s->check_type > XZ_CHECK_CRC32)
                return XZ_UNSUPPORTED_CHECK;
 #else
--
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