[xen staging-4.20] ns16550: harden name/value pair parsing

[patchbot@xxxxxxx]

commit 928144f39f9195794e4aec147144238b242d49a7
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Apr 20 12:35:56 2026 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Apr 20 12:35:56 2026 +0200

    ns16550: harden name/value pair parsing
    
    strsep(), unless passed a 1st argument which itself points at a NULL
    pointer, won't return NULL. Instead if the separator(s) looked for isn't
    found, that pointed-to field would be updated to hold NULL. Hence the
    important check in get_token() is for token to be non-NULL after the call
    (which get_token()'s callers rely upon), while the checking of param_name
    is left there just in case.
    
    Fixes: 97fd49a7e074 ("ns16550: add support for UART parameters to be 
specifed with name-value pairs")
    Reported-by: Kamil Frankowicz <kamil.frankowicz@xxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: b27d3b45c75cf378f06ed72758c034a5d0f8d560
    master date: 2026-04-07 13:53:49 +0200
---
 xen/drivers/char/ns16550.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index 9507af299f..ea35caf034 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -1454,7 +1454,7 @@ static enum __init serial_param_type get_token(char 
*token, char **value)
     unsigned int i;
 
     param_name = strsep(&token, "=");
-    if ( param_name == NULL )
+    if ( !param_name || !token )
         return num_serial_params;
 
     /* Linear search for the parameter. */
--
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