Unverified Commit 25524b61 authored Nov 11, 2025 by Armin Wolf Committed by Ilpo Järvinen Nov 18, 2025

fs/nls: Fix utf16 to utf8 conversion



Currently the function responsible for converting between utf16 and
utf8 strings will ignore any characters that cannot be converted. This
however also includes multi-byte characters that do not fit into the
provided string buffer.

This can cause problems if such a multi-byte character is followed by
a single-byte character. In such a case the multi-byte character might
be ignored when the provided string buffer is too small, but the
single-byte character might fit and is thus still copied into the
resulting string.

Fix this by stop filling the provided string buffer once a character
does not fit. In order to be able to do this extend utf32_to_utf8()
to return useful errno codes instead of -1.

Fixes: 74675a58 ("NLS: update handling of Unicode")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://patch.msgid.link/20251111131125.3379-2-W_Armin@gmx.de


Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

parent 39ae6c50

fs/nls/nls_base.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -94,7 +94,7 @@ int utf32_to_utf8(unicode_t u, u8 *s, int maxout)

		l = u;
		if (l > UNICODE_MAX \|\| (l & SURROGATE_MASK) == SURROGATE_PAIR)
		return -1;
		return -EILSEQ;

		nc = 0;
		for (t = utf8_table; t->cmask && maxout; t++, maxout--) {
		@@ -110,7 +110,7 @@ int utf32_to_utf8(unicode_t u, u8 *s, int maxout)
		return nc;
		}
		}
		return -1;
		return -EOVERFLOW;
		}
		EXPORT_SYMBOL(utf32_to_utf8);

		@@ -217,8 +217,16 @@ int utf16s_to_utf8s(const wchar_t *pwcs, int inlen, enum utf16_endian endian,
		inlen--;
		}
		size = utf32_to_utf8(u, op, maxout);
		if (size == -1) {
		if (size < 0) {
		if (size == -EILSEQ) {
		/* Ignore character and move on */
		continue;
		}
		/*
		* Stop filling the buffer with data once a character
		* does not fit anymore.
		*/
		break;
		} else {
		op += size;
		maxout -= size;