From: Anton Moryakov <ant.v.moryakov@gmail.com>
To: linux-mtd@lists.infradead.org
Cc: David Oberhollenzer <david.oberhollenzer@sigma-star.at>,
Anton Moryakov <ant.v.moryakov@gmail.com>
Subject: [PATCH] nftl_format: prevent unsigned underflow in INFTL virtual unit calculation
Date: Tue, 27 Jan 2026 15:31:00 +0300 [thread overview]
Message-ID: <20260127123100.47486-1-ant.v.moryakov@gmail.com> (raw)
When formatting an INFTL partition, the code computes:
numvunits = (ezones - 2) * PERCENTUSED / 100;
If ezones < 2 (e.g. due to user specifying start offset >= device size),
this causes an unsigned underflow, leading to a huge and invalid numvunits.
Add a guard to ensure ezones >= 2 before subtraction. If not, abort with
an error message, as a valid INFTL partition requires at least two erase
blocks for media headers.
Signed-off-by: Anton Moryakov <ant.v.moryakov@gmail.com>
---
nand-utils/nftl_format.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/nand-utils/nftl_format.c b/nand-utils/nftl_format.c
index c8b8b50..3667be3 100644
--- a/nand-utils/nftl_format.c
+++ b/nand-utils/nftl_format.c
@@ -371,6 +371,8 @@ int main(int argc, char **argv)
maxzones = meminfo.size / meminfo.erasesize;
pezstart = startofs / meminfo.erasesize + 1;
pezend = startofs / meminfo.erasesize + ezones - 1;
+ if (ezones < 2)
+ exit(EXIT_FAILURE);
numvunits = (ezones - 2) * PERCENTUSED / 100;
for (ezone = pezstart; ezone < maxzones; ezone++) {
if (BadUnitTable[ezone] != ZONE_GOOD) {
--
2.39.2
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