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dix: avoid null ptr deref at doListFontsAndAliases

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In the `doListFontsAndAliases` function in dixfonts.c, when a font alias
is encountered (`err == FontNameAlias`) as a result of
`list_next_font_or_alias` call, the code allocates memory for
`resolved` variable (`resolvedlen + 1` bytes) for storing target font
name. In this case, if the `malloc(resolvedlen + 1)` call fails,
`resolved` remains NULL.

Later, when check (`else if (err == FontNameAlias)`) is TRUE, the code
uses `memcpy` to copy nullable `resolved` into `tmp_pattern` without
checking if `resolved` is NULL, so there is a potential null ptr
dereference.

This commit replaces `malloc` with `XNFalloc` for allocating memory for
`resolved`. `XNFalloc` will internally check result of `malloc` and stop
program execution if allocation was failed, preventing potential NULL
dereferencing.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Mikhail Dmitrichenko <m.dmitrichenko222@gmail.com>
(cherry picked from commit 0237462d32)

Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2151>
This commit is contained in:
Mikhail Dmitrichenko 2025-12-17 11:15:27 +03:00 • committed by Marge Bot
parent 70f5424e54
commit e6696a43a5
1 changed files with 2 additions and 3 deletions
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5
dix/dixfonts.c
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@ -639,9 +639,8 @@ doListFontsAndAliases(ClientPtr client, LFclosurePtr c)
}
if (err == FontNameAlias) {
free(resolved);
resolved = malloc(resolvedlen + 1);
if (resolved)
memcpy(resolved, tmpname, resolvedlen + 1);
resolved = XNFalloc(resolvedlen + 1);
memcpy(resolved, tmpname, resolvedlen + 1);
}
}